Self-assembled oxide films with tailored nanoscale ionic and electronic channels for controlled resistive switching

Transcription

1 Reeive 19 Fe 2016 Aepte 24 Jun 2016 Pulishe 5 Aug 2016 DOI: /nomms12373 OPEN Self-ssemle oxie films with tilore nnosle ioni n eletroni hnnels for ontrolle resistive swithing Seungho Cho 1, *, Cho Yun 1, *, Stefn Tppertzhofen 2, Ahme Kursumovi 1, Shinuhm Lee 1, Ping Lu 3, Qunxi Ji 4, Meng Fn 5, Jie Jin 5, Hiyn Wng 5,6, Stephn Hofmnn 2 & Juith L. MMnus-Drisoll 1 Resistive swithes re non-voltile memory ells se on nno-ioni reox proesses tht offer energy effiient evie rhitetures n open pthwys to neuromorphis n ognitive omputing. However, hnnel formtion typilly requires n irreversile, not well ontrolle eletroforming proess, giving iffiulty to inepenently ontrol ioni n eletroni properties. The evie performne is lso limite y the inomplete unerstning of the unerlying mehnisms. Here, we report novel memristive moel mteril system se on self-ssemle Sm-ope CeO 2 n SrTiO 3 films tht llow the seprte tiloring of nnosle ioni n eletroni hnnels t high ensity (B2 inh 2 ). We systemtilly show tht these evies llow preise engineering of the resistne sttes, thus enling lrge on off rtios n high reprouiility. The tunle struture presents n iel pltform to explore ioni n eletroni mehnisms n we expet wie potentil impt lso on other nsent tehnologies, rnging from ioni gting to miro-soli oxie fuel ells n neuromorphis. 1 Deprtment of Mterils Siene n Metllurgy, University of Cmrige, 27 Chrles Bge Ro, Cmrige CB3 0FS, UK. 2 Deprtment of Engineering, University of Cmrige, 9 J.J. Thomson Avenue, Cmrige CB3 0FA, UK. 3 Sni Ntionl Lortory, Aluquerque, New Mexio 87185, USA. 4 Center for Integrte Nnotehnologies, Los Almos Ntionl Lortory, Los Almos, New Mexio 87545, USA. 5 Deprtment of Eletril n Computer Engineering, Texs A&M University, College Sttion, Texs 77843, USA. 6 Shool of Mterils Engineering, Purue University, West Lfyette, Inin 47907, USA. * These uthors ontriute eqully to this work. Corresponene n requests for mterils shoul e resse to J.L.M.-D. (emil: jl35@m..uk). NATURE COMMUNICATIONS 7:12373 DOI: /nomms

2 NATURE COMMUNICATIONS DOI: /nomms12373 Arnge of emerging non-voltile rnom-ess memory tehnologies for fster, higher ensity n low energy memory re now eing explore worlwie to overome the emerging hllenges of sle, spee n energy of toy s flsh floting-gte metl-oxie-semionutor fiel-effet trnsistor tehnology se on silion. Among them, resistive rnom ess memory (ReRAM, lso terme s memristive evie) is one of the promising nites for the future non-voltile rnom-ess memory. ReRAM hs the potentil for high-ensity integrtion, fst opertion, low-power onsumption, n frition omptiility with silion omplementry metloxie-semionutor tehnology 1. In ition, y mimiking iologil neurons, memristive evies hve the potentil to omine logi þ memory opertions n hene re of interest in future ognitive omputing 2. Metl oxie resistive swithing strutures hve een wiely stuie for ReRAM. They hve severl vntges over phse hnge memories, ferroeletri RAMs n mgnetoresistive RAMs (ref. 3), ut still there is lk of reprouiility in their properties. They lso typilly exhiit lower enurne thn the forementione lterntives n nee high-voltge (5 20 V) eletroforming proess 4,5. The unerstning of memristive swithing in oxie mterils is lso inomplete. Vrious moels hve een propose suh s filmentry onution, hrge trpping efets sttes, trp-ontrolle spe-hrge-limite urrent n hnge of Shottky-like rrier 3,6. In ft, these effets re not mutully exlusive, the essentil feture of ll of the forementione moels eing the migrtion of oxygen vnies n eletrons uner n pplie eletri fiel 3,7 11. For vlene hnge resistive swithing, the unesire ut essentil eletroforming proess whih inues rnom filmentry onution hnnels in oxie films inues reox retion leing to reution of the oxygen ontent in the film to form positively hrge oxygen vnies plus neutrlizing eletroni rriers 5,8, However, the oupling of the ions n eletrons mkes the unerstning of the resistive swithing mehnism unler. Also, it is iffiult to inepenently ontrol ioni n eletroni properties of suh hnnels n the stohsti nture of the eletroforming proess mkes the unerstning of the swithing proess more iffiult. To strongly vne the unerstning of resistive swithing, we propose struture in whih ioni n eletroni hnnels re eouple into seprte hnnels n eletroforming is inherently not require. Hene, this work is fouse on engineering n testing suh struture s moel mteril system. This ws one through reting vertil heteroepitxil nnoomposite (VHN) films. We show tht unique n highly tunle memristive properties result in whih the eletroni urrent is ontrolle y the ioni vny onentrtion in the ioni nnohnnels. The struture llows informtion to e enoe in the onfine ioni nnohnnels whih is loser to nture s purely ionilly se informtion trnsfer of hemil synpses n hene gives promise for future ognitive omputing evies. 50 Sm-ope CeO 2 (SDC): 50 SrTiO 3 (STO) (tomi rtios of Sm to Ce: 0, 0.1, 0.2 n 0.3 in SDC) ws hosen s the moel nnoomposite system to stuy. In this system, SDC nnoolumns ply the ioni role, n the vertil interfes etween SDC n STO ply the eletroni role in resistive swithing. SDC is well-known oxygen ioni onutor with tunle vny onentrtion epening on the Sm oping level Reently, we isovere high temperture (from 360 to 673 K) ioni onution in SDC:STO nnoomposites, whih grow very esily y self-ssemly from single-pulse lser eposition trget 18.It ws foun tht very fst onution SDC ioni nnopillrs forme in the STO film mtrix. On the other hn, the resistive swithing ehviour of the SDC:STO strutures ws not explore efore. Here, t room temperture, we exploit the high ioni onution in the SDC nnopillrs s well s eletroni onution t the SDC/STO interfe, to form, for the first time, seprte ioni n eletroni nnohnnel evie. In these strutures, to tune the Shottky rrier we moify the nnopillr ioni onution y using ifferent Sm oping levels in the SDC. We emonstrte tht the SDC:STO strutures re eletroforming-free with high enurne. Moreover, we emonstrte for the first time tht the onentrtion of moile oxygen vnies preisely ontrols the low-resistne stte (LRS). The novel strutures hve wie pplition eyon resistive swithing to other eletronis n energy ionotroni tehnologies where vertil, fst ioni or tunle mixe (ioni n eletroni) onution is require, for exmple, soli stte ioni gting, fuel ell thoes n neuromorphi omputing 19. Results Formtion of SDC:STO vertil heteroepitxil nnoomposites. We first present the results of n optimum film (in terms of resistive swithing): 20 t.% SDC:STO VHN film grown on 0.5 wt.% N-ope SrTiO 3 (N:STO), using film growth rte of 3 nm s 1 y pulse lser eposition. As we show lter, 20% Sm is the optimum oping onentrtion for the highest ioni onution (highest moile vny onentrtion), n lso tht growth rte is importnt for ontrolling rystlline perfetion, oth of these ftors eing very importnt for optiml evie performne. Figure 1, show snning trnsmission eletron mirosopy (STEM) high-ngle nnulr rk-fiel (HAADF) imges in ross-setionl view n pln view, respetively, initing phse seprtion n vertilly ligne phses (see lso Supplementry Fig. 1). The higher tomi numer phse, nmely the SDC, is righter thn STO. Figure 1 is highly mgnifie HAADF imge of n SDC/STO interfe, showing n tomi-sle shrp n epitxil interfe with n orienttionl reltionship tht the SDC [001] xis is prllel to the STO [001] xis n the SDC [100] xis is prllel to the STO [110] xis. The three-imensionl lignment nture of the VHN films ws stuie using four-irle X-ry iffrtion (XRD). The XRD o-2y sn of 20 t.% SDC:STO VHN film with nominl thikness of B200 nm on N:STO shows only (00l) peks of SDC n STO (Fig. 1) without tres of other phses or orienttions, onfirming their high egree of rystllogrphi orienttion n no intermixe rystlline phses. The lttie onstnts of ulk ui SDC n STO re Å in JCPDS # n Å in JCPDS # , respetively. Thus, the SDC nnopillrs re grown on the N:STO sustrte with n energetilly fvourle 45 in-plne rottion to minimize in-plne lttie mismth (1.6%), s shown y the j-sn (Fig. 1e). For the SDC:STO film on the N:STO further struturl informtion ws otine from reiprol spe mps (RSMs) roun STO(2 03)(Fig.1f).The SDC(2 2 4)pek ws oserve in the lower q z region thn the (2 03) pek of the STO. The out-of-plne n the in-plne lttie prmeters of SDC were lulte to e n Å, respetively, from omintion of the o-2y sn n the RSM, orresponing to moerte ompression long the out-of-plne iretion (5%) n moerte expnsion long the in-plne iretion (0.18%). Figure 1g shows rystllogrphi moel of the vertil SDC(100)//STO(110) interfe se on the STEM n XRD nlyses. Resistive swithing ehviour in nnoomposite-se evie. Figure 2, show shemti illustrtion for (Pt (top)/20 t.% SDC:STO VHN film (nominl thikness: 30 nm)/n:sto (ottom)) evie n repete R V sns of the evie, 2 NATURE COMMUNICATIONS 7:12373 DOI: /nomms

3 NATURE COMMUNICATIONS DOI: /nomms12373 ARTICLE S S S S D T D T C O C O [001] Intensity (ps) STO (002) STO (001) STO (003) SDC (002) SDC (004) STO SDC θ (Degree) STO SDC e f g SDC (111) 7.7 High Intensity (.u.) STO (111) (Degree) q z (nm 1 ) STO (203) 7.3 SDC (224) q x (nm 1 ) Low Intensity (.u.) Sr Ce/Sm Ti O Figure 1 Struturl hrteriztions of VHN. Struturl properties of 20 t.% SDC:SrTiO 3 (STO) VHN from 3 nm s 1 growth rte whih ws the optimize film from the point of view of high on/off rtio on resistive swithing. (,) Phse orering in ross-setionl view n pln view of SDC:STO, s revele y STEM HAADF imges. Sle rs, 30 nm. () High-resolution HAADF imge of the vertil interfe. Sle r, 2 nm. () XRD o-2y sn of SDC:STO nnoomposite film. (e) 360 j-sns of the (111) pek of STO n the (111) pek of SDC. (f) RSM roun the STO(-203) refletion. (g) Crystllogrphi moel of SDC:STO VHN roun vertil interfe etween SDC n STO. respetively. For ll the eletril mesurements, ipolr voltge signls were pplie to the irulr top Pt eletroe with imeter of 50 mm while the ottom N:STO eletroes were groune. The evie exhiite non-voltile resistive swithing s funtion of voltge (V). An eletroforming proess is not require for reprouile resistive swithing properties. One of the urves shown in Fig. 2 ws the first sn from the pristine stte whih ws lmost the sme s the suessive R V urves. The evie ws swithe to LRS y pplying negtive is n swithe to high-resistne stte (HRS) y pplying positive is. This ounterlokwise resistne vrition hs een reporte for numer of oxygen vny migrtion-se resistive swithing systems The evie exhiite uniform resistne vritions for over -yles (Fig. 2 with lterntive voltge pulses of 5 n þ 5 V for swithing n re voltge of 0.3 V), n retention of the originl resistne stte without egrtion (Fig. 2). In ontrst to these evies, plin SDC n STO films require eletroforming proesses for reversile resistive swithing n fter eletroforming they showe lower on off rtios n poorer enurne (Supplementry Fig. 2). XRD o-2y sns for n SDC film n n STO film on N:STO re provie in Supplementry Fig. 3. To stuy onution n resistive swithing mehnisms in the VHN films, we ompre optimize VHN films n plin films forme from iniviul phses t first. Before eletroforming, the plin film strutures: [Pt/20 t.% SDC film/n:sto] n [Pt/STO film/n:sto] oth showe symmetri n retifying I V hrteristis (Fig. 3,, respetively), s expete. The results re onsistent with tht expete for Shottky-like rriers on top eletroe interfes euse SDC n STO re n-type mterils, Pt is high work-funtion metl n the ottom interfe with N:STO sustrte is n ohmi ontt 3,10,11,20. Turning now to the se of the Pt/SDC:STO VHN/N:STO evies, the SDC nnoolumns n the STO mtrix re n-type semionutors n their vertil interfe regions re lso n-type oxies ue to the high onentrtion of oxygen vnies 20. Thus, y onsiering only these fts (not tking into ount the presene of moile oxygen vnies), symmetri I V urves of the VHN struture woul e expete to e similr to those oserve for the plin SDC n STO evies. Uner smll pplie is, n symmetri n retifying hrteristi ws shown (Fig. 3). The highly symmetri I V urve inites n interfe-limite onution of the VHN evie rther thn ulk-limite onution. There re four min kins of interfe-limite onution mehnisms: Shottky emission, iret tunnelling, Fowler-Norheim tunnelling n interfelimite trp-ssiste tunnelling 21,22. The iret tunnelling n Fowler-Norheim tunnelling n e rule out in our se euse our oxie lyers re thik (Z30 nm). The urrent ensity ross Shottky rrier for n pplie is voltge V J ¼ A T 2 exp e f p n ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi 3 ev=4pe r e ð1þ k B T where A is the effetive Rihrson onstnt, T is the solute temperture, k B is Boltzmnn s onstnt, e is the eletron hrge, ef n is the height of the Shottky rrier, e r is the ieletri onstnt of the film, e 0 is the permittivity of free spe n is the smple thikness. If Shottky rrier ontrols the urrent, NATURE COMMUNICATIONS 7:12373 DOI: /nomms

4 NATURE COMMUNICATIONS DOI: /nomms12373 STO SDC Pt N:STO sustrte A Eletroforming-free 20 times repetition Voltge (V) Current (A) SDC Current (A) STO Voltge (V) Voltge (V) HRS LRS 2 HRS LRS Retention time (h) Figure 2 Resistive swithing of VHN-se evie. () Shemti of the mesurement onfigurtion of SDC:SrTiO 3 (STO) VHN evie. () Eletroforming-free R V hysteresis loops in SDC:STO VHN evie. () Uniform resistne vrition with repete eletril yles. () The retention hrteristis of oth resistne sttes. semilog plots of J/T 2 (or I) versus V 1/2 n e fitte y stright line. The semilog plot of I versus V 1/2 for the VHN evie inee shows stright line fit (Supplementry Fig. 4). In ition, ler non-liner reltionship etween log I versus V 1 rules out the trp-ssiste tunnelling mehnism 24. Therefore, in the SDC:STO VHN evie, the intrinsi onution in the HRS is minly governe y Shottky emission. Interestingly, s the solute vlue of negtive is inrese, the urrent rmtilly inrese, resulting in ompletely ifferent I V urve shpe (Fig. 3) from the smll pplie is se (Fig. 3). In ition, the I V sn with n pplie is rnge of ±2V showe ler hysteresis. Figure 3 shows tht the urrent in the VHN evie ws 2 4 orers of mgnitue higher thn in the plin STO n SDC evies (with the sme film thikness), respetively, using the sme voltge mplitues. This inites tht the interfe etween the Pt n VHN vertil interfes hs nrrower rrier with n/or lower rrier height thn those of plin films euse eletroni onution in oth plin n VHN ses re minly governe y Shottky emission 20,25. This is supporte y onutive tomi fore mirosopy (-AFM) mesurements initing higher eletroni onutivity long the vertil hetero-interfes of the VHN film (Supplementry Fig. 5). Eletroni onution of STO n e esily tune, mong other oxies, y hemil oping of smll mount of opnts or y inresing oxygen vny onentrtions The most likely reson for the higher onutivities of the STO:SDC vertil interfes is higher onentrtion of oxygen vnies long the vertil interfes y struturl mismth of the two mterils Current (A) Low V SDC:STO VHN SDC:STO VHN Voltge (V) Voltge (V) (STO: perovskite, ¼ nm, SDC: fluorite, ¼ nm) thn tht of the ulk STO prt, leing to higher rrier ensities long the vertil interfes 20 (Supplementry Fig. 6). We note tht in the VHN system, ionilly onuting 18 n eletronilly insulting vertil SDC nnoolumns re emee in n ionilly n eletronilly insulting, ut interfilly eletronilly onuting, SrTiO 3 (STO) mtrix. Devie reepenent-resistne vlues were mesure (Supplementry Fig. 7). It ws foun the resistne vlues in HRS n LRS erese with inresing Pt eletroe re, whih is onsistent with the ft tht our evies hve uniformly istriute eletroni nnohnnels. To investigte the moultion of the Shottky rrier etween the SDC STO interfe n the Pt eletroe, we extrte the rrier height, ef n ¼ k B T ln(a T 2 /J o ), where J o is sturtion urrent ensity, from I V urves with ifferent tempertures (293, 313, 333 n 353 K) 31,32. For simpliity, we use the effetive Rihrson onstnt of A ¼ 120 A m 2 K 2. The inresing solute vlue of the negtive sweep voltge use the rrier height (with positive is) to erese (Supplementry Fig. 8), whih implies tht the oxygen vny umultion t the top interfe is the use of the rrier height erese. Seprte ioni n eletroni nnohnnel moel. Bse on the forementione results, we propose seprte ioni n eletroni nnohnnel moel for the resistive swithing mehnism of SDC:STO VHN (SDC: ioni nnohnnel, SDC STO vertil interfe: eletroni nnohnnel)-se evies. Overll, the oserve resistive swithing ehviour in the SDC:STO VHN evie n e expline y the moultion of the interfil eletroni rrier forme on the interfe etween the top Pt eletroe n VHN film ue to the migrtion of oxygen vnies to or wy from the top Pt eletroe uner the pplie eletri fiel. Figure 4 shows seprte ioni n eletroni nnohnnel moel for resistive swithing of the SDC:STO VHN film evie. The simplifition of shemti showing ross-setionl SDC:STO VHN film evie y isring ulk Current (A) High V Figure 3 I V urves of evies efore eletroforming. () Plin 20 t.% SDC film evie. () Plin SrTiO 3 (STO) film evie. (,) 20 t.% SDC:STO VHN firm evie. 4 NATURE COMMUNICATIONS 7:12373 DOI: /nomms

5 NATURE COMMUNICATIONS DOI: /nomms12373 ARTICLE Aitionl oxygen vnies (AOV) 2 Low negtive is SLB with (W) n height (H) erese y AOV, W erese y negtive is HRS Metl-to-semionutor rrier (e n ) uner negtive is semionutor-to-metl rrier (ev i ) uner positive is No is 1 metl Ner top eletroe interfe HRS Shottky-like rrier (SLB) t metl-nnoomposite interfe Nnoioni hnnel Nnoeletroni hnnel 3 High negtive is High positive to no is More erese in SLB W n H HRS LRS Reovery of SLB y erese in positive is n AOV removl LRS HRS 4, 5 High negtive to no is Voltge (V) 7 High positive is SLB still smll y memory effet of oxygen vny position LRS 6 Low positive is AOV still on top n SLB influene y oth AOV on top n positive is LRS AOV signifintly reue ut not effetive reovery of SLB euse of high positive is LRS Figure 4 Seprte ioni n eletroni nnohnnel moel. Shemti igrm of seprte ioni n eletroni nnohnnel moel for resistive swithing of the SDC:SrTiO 3 VHN film evie. The simplifition of SDC:SrTiO 3 VHN film evie is epite in Supplementry Fig. 9. HRS, high-resistne stte; LRS, low-resistne stte. STO prts is epite in Supplementry Fig. 9. The simplifition is se on the following fetures. First, the plin SDC n plin STO showe muh lower eletroni onutivities thn the nnoomposite se n require the eletroforming proesses for the reversile resistive swithing ehviours (Fig. 3 n Supplementry Fig. 2). Seon, the eletronilly onutive hnnels in the SDC:STO nnoomposite evies re the vertil interfes of SDC n STO, s shown in Supplementry Fig. 5. The ulk STO n SDC prts re more eletronilly insulting ompre with their vertil interfes. Thir, from the ioni point of view, the ioni onutivities of ulk STO in the SDC:STO vertil nnoomposite films re muh lower thn those of the SDC prts (SDC olumns) 18. Assuming n iel interfe, without Fermi pinning, eletrons fe metl-to-semionutor rrier, ef n ¼ e(f m w), where f m is the metl work funtion n w is the semionutor eletron ffinity, uner negtive is n semionutor-tometl rrier, ev i ¼ e(f m f s ) ¼ ef n (E C E F ), where f s, E C n E F re the work funtion, the onution n minimum n the Fermi level of the semionutor, respetively, uner positive is for eletroni onution. We efine these interfe eletroni rriers s Shottky-like rriers (Fig. 4 n Supplementry Fig. 6). If we ssume tht there is no moile opnt (oxygen vny) whose position is influene y the externl eletri is n fully eplete region, in the negtive is onition, V i inreses while the rrier with ereses n f n remins onstnt. In the positive is onition, V i ereses while the rrier with inreses n f n still remins onstnt. In the following we ssume tht the oxygen vny onentrtion t the Pt/nnoeletroni interfe is mnipulting the epletion with of Shottky rrier 33. When smll negtive is is pplie, the with n height of the Shottky-like rrier ereses y oxygen vny umultion t the eletroe-nnoomposite interfe. The negtive is lso ereses the rrier with. As the solute vlue of the negtive is inreses, the rrier with n height ereses further, using the evie to go into the LRS. Although the solute vlue of negtive is ereses, the rrier is still smll owing to the memory effet of oxygen vny positions euse there is no strong riving fore for oxygen vny migrtion towrs the ottom eletroe. When smll positive is is pplie to the evie, itionl oxygen vnies re still on top ue to the memory effet. Thus, the rrier is influene y oth oxygen vnies on the top interfe n the positive is, whih mintins the LRS of the nnoomposite evie. As the solute vlue of the positive is inreses, the oxygen vny umultion is signifintly reue. However, the rrier is not effetively reovere euse of the high positive is. The rrier is influene y oth the removl of the umulte oxygen vnies n the positive is, ompetitively. When the solute vlue of positive is ereses, the rrier is influene only y erese in the positive is euse there is no oxygen vny umultion on the interfe etween the top Pt eletroe n VHN film. Thus, the rrier height is reovere y erese in the positive is, leing to the HRS of the evie. Cyli I-V sns of self-ssemle SDC:STO VHN evies lerly exhiit oxygen vny effets s n e seen from the voltge-epenent resistne ehviour (Fig. 4). While the results isusse ove unerline the importne of oxygen vnies on resistive swithing, to efinitively prove n quntify their role, ifferent opnt (Sm 3 þ ) onentrtions in the SDC omponent (ioni hnnel) of the films were stuie to inue ifferent ioni onutivities (moile oxygen vny onentrtions). Figure 5 show resistne vlues of the HRS NATURE COMMUNICATIONS 7:12373 DOI: /nomms

6 NATURE COMMUNICATIONS DOI: /nomms12373 CeO 2 -STO 10 t.% Sm-ope CeO 2 -STO t.% Sm-ope CeO 2 -STO 30 t.% Sm-ope CeO 2 -STO e 10 4 R in LRS σ ioni in ref Atomi rtio of Sm to Ce σ ioni (10 2 Ω 1 m 1 ) Figure 5 Tuning of resistne vlues in LRS. Resistne vrition with repete eletril yles (with pplie voltges of 5 n þ 5 V for swithing n re voltge of 0.3 V) of CeO 2 :SrTiO 3 VHN film evies with ifferent opnt (Sm 3 þ ) onentrtions in CeO 2 :() 0 t.% Sm. () 10 t.% Sm. () 20 t.% Sm. () 30 t.% Sm. (e) Resistne vlues in LRS s funtion of opnt onentrtions (lose irles). Error rs re provie s s.. We inlue the ioni onutivity (s ioni ) vlues for the films with ifferent opnt onentrtions reporte in the literture 15 (open squres). n the LRS of 0, 10, 20 n 30 t.% SDC:STO VHN films, respetively uner lternting pulses of þ 5 n 5 V. These films ll exhiite eletroforming-free resistive swithing properties. It is oserve tht the HRS vlues re very lose (to within 15%) for ll the ompositions stuie in this work, s shown in Fig. 5 (n Supplementry Fig. 10). Oxygen vnies re eplete t the interfes etween Pt n VHN films y pplying the high positive ises in ll the evies. Thus, the resistne vlues in HRS uner high positive ises were similr regrless of intrinsi oxygen vny onentrtions on the VHN films with the ifferent Sm 3 þ ontents. On the other hn, the LRS vlues erese when the Sm oping rtios inrese from 0 to 20% n then inrese gin when the oping rtios inrese to 30%. Figure 5e shows tht there is iret inverse orreltion of LRS with ioni onutivity. The ioni onutivity t 600 C ws use 15. The vlues elow 600 C, s is pplile for our mesurements, sle with oping onentrtion in the sme orer s tht of the high temperture t 15. We note tht there will e some Joule heting effets giving very lol temperture rises for further enhne ioni onution 20. At 30 t.%, Sm efet ssoition les to erese in moile oxygen vny onentrtion n hene is onsistent with the rise in the resistne vlue of LRS for this highest oping level 34. Hene, the role of oxygen vny onentrtion on LRS is inee lerly proven. Overll, the effet of tuning of the resistne of the LRS while keeping the resistne of the HRS onstnt is tht the on off rtio is preisely ontrolle (Supplementry Fig. 10). The mximum on off rtios hieve re high t B10 4 n re suffiient for prtil memory pplitions 33. Effet of film growth rte on evie performne. Finlly, the proof of the nee for oth high ioni onutivity n high qulity vertil eletroni onuting hnnels to give forming-free, high enurne n tunle on off rtio evies is me systemtilly y eliertely reuing perfetion in the strutures. This ws one y inresing film growth rte from 3 to 0.50 nm s 1. The growth rtes re lelle (for the slowest growth rte) to Rte 4 (for the fstest growth rte). As the growth rtes inrese, the nnoolumn withs erese s shown in AFM imges (Fig. 6). TEM ross-setion imges of the SDC:STO VHNs (Fig. 6 for Rte 2 n 6 for Rte 4) onfirme smller with olumns of SDC in the STO mtries (Fig. 6,e). In thin-film growth proess, the most thermoynmilly stle phses (tking into ount epitxil stiliztion) will grow on the sustrte uring eposition n ooling 35. There re ifferent phse seprtion mehnisms; nuletion n growth, spinol growth n pseuo-spinol growth epening on the hemil misiility. In the nuletion n growth mehnism of immisile two phses, the phse with higher interfil energy with the sustrte forms nuletion islns tht grow into olumns, wheres the other phse with lower interfil energy unergoes lyer-y-lyer growth n eomes the plin mtrix 36. A higher growth rte les to shorter resting time t of growth unit n hene shorter growth unit iffusion length on sustrte, resulting in smller nuletion islns, n onsequently smller olumn withs. The iffusion length of growth unit n e roughly estimte y 37 p L 2 ffiffiffiffiffiffi Dt, where D stns for iffusion oeffiient n t for iffusion time. Thus, if the ominnt growth mehnism is the iffusion-ontrolle nuletion n growth, plot of olumn with versus (growth rte) 1/2 will show stright line fits to the t. Our t grees well with the iffusion length eqution (Supplementry Fig. 11), whih is strong eviene of iffusion-ontrolle nuletion n growth mehnism of the SDC:STO VHNs. High-resolution TEM imges (Supplementry Fig. 12) showe less perfet lttie struture thn the lower growth rte ses. Figure 6f shows XRD o-roking urves of SDC(002) peks of the VHN films eposite t ifferent growth rtes. Higher growth rtes le to higher full with t hlf mximum vlues in the o-roking urves initing more tilte ioni n eletroni hnnels n their egrtion of the rystllinity, onsistent with the TEM results. Figure 7 shows tht eletroforming-free resistive swithing ehviour is only oserve for the slowest grown smples whih re the most ligne, highly rystlline smples with high ioni onutivity (high onentrtion of moile oxygen vnies). Inee, Fig. 7, show the resistne vlues of pristine sttes t room temperture n the ioni onutivity (otine from impene spetrosopy mesurements) for the ifferent growth rtes, respetively, showing lerly the smples grown t lower rtes hve higher eletroni n ioni onutivity ( higher onentrtion of moile oxygen vnies). In the se of the two fstest grown smples, even fter the eletroforming proess, low on off rtios n poor enurne were exhiite, s shown in Fig. 7,e. Hene, the results lerly show tht high performne memristive evies re hieve only when films hve high 6 NATURE COMMUNICATIONS 7:12373 DOI: /nomms

7 NATURE COMMUNICATIONS DOI: /nomms12373 ARTICLE Growth rte inrese Rte 2 Rte 3 Rte 4 Rte 2 Rte 4 e Column with STO mtrix S C S C Sustrte Sustrte N:STO sustrte SDC olumn Column with (nm) Column with FWHM Rte 2 Rte 3 Rte Growth rte (nm s 1 ) FWHM (Degree) f Intensity (.u.) Intensity (.u.) Δω (Degree) Rte 3 FWHM ~1.52 FWHM ~2.01 Intensity (.u.) Intensity (.u.) Rte 4 Rte 2 FWHM ~ Δω (Degree) FWHM ~ Δω (Degree) Δω (Degree) Figure 6 Struturl hrteriztions of VHN eposite from ifferent film growth rtes. () Atomi fore mirosopy imges of 20 t.% SDC:STO VHN films eposite from ifferent film growth rtes. Sle rs, 20 nm. (,) Cross-setionl STEM HAADF imges of SDC:STO VHN films grown from Rte 2 n Rte 4, respetively. S n C stn for STO n SDC, respetively. Sle rs, 20 nm. () Column withs n full with t hlf mximum (FWHM) vlues in o-roking urves of SDC:STO VHN films s funtion of film growth rtes. Error rs re provie s s.. (e) Typil epition of SDC:STO VHN film on N-ope STO sustrte, in whih the SDC olumns re emee in n STO mtrix. (f) XRD o-roking urves of SDC:STO VHN films eposite from ifferent film growth rtes. onentrtion of moile oxygen vnies in the ioni SDC hnnels n when the ioni (SDC) n eletroni hnnels (vertil interfes) re well rystllize, highly ligne n onnete through the film thikness. Disussion A novel soli stte ioni memristive omposite oxie thin-film system ws esigne n emonstrte. These films, ompose of seprte ioni n eletroni nnohnnels gve eletroformingfree resistive swithing evies with highly tunle LRS n high HRS/LRS resistne rtios (B10 4 ). High swithing vriility etween ifferent evies omine with smll HRS/LRS resistne rtios s shown y the mjority of oxie ReRAMs, usully B10 to 10 2 (ref. 38), hve reently lle the ppliility of onventionl oxie ReRAMs for memory rrys into question 39.Forming-free ReRAMs with low vriility n high on/off rtios, s shown y our evies, re therefore iel moel-systems for resistive swithes. The LRS ws shown to orrelte iretly with the moile oxygen vny onentrtion (ioni onutivity) in the SDC n ws preisely tune y vrying the Sm oping level in the SDC. This tuning enle high on off rtios to e hieve. The evie performne ws improve signifintly ompre to the plin SDC film- n STO film-se evies whih require high-voltge forming proesses n hve prolems of reprouiility n enurne. Integrtion of memory evies in ense memory rrys is hllenging for onventionl oxie ReRAMs whih rely on eletroforming proesses. After evie frition, eh evie nees to e forme seprtely in ontrolle mnner ue to the lrge evition of the forming voltges usully oserve. Moreover, the evie prmeters of ess trnsistors (suh s hnnel length/with n gte oxie thikness) to selet iniviul memory ells nee to e mthe to the high forming voltges. Therefore, the esign of forming-free oxie ReRAMs is lso highly esirle from prtil point of view. The form of I V hrteristis oul e expline very lerly y invoking oxygen vny migrtion effets. The strightness n perfetion of the ioni n eletroni nnohnnels ws shown to e ritil to the evie performne. Nnoompositese mirosle evies were emonstrte. To test the fesiility of nnosle evies, we mesure I V yles using -AFM tip on vertil interfe of the SDC:STO VHN film on the N:STO sustrte (Supplementry Fig. 13). Reversile NATURE COMMUNICATIONS 7:12373 DOI: /nomms

8 NATURE COMMUNICATIONS DOI: /nomms12373 Eletroforming free e no yes FWHM of ω-roking urve (Degree) 10 8 Rte Rte Growth rte (nm s 1 ) Rte 2 Eletroforming-free 10 2 After eletroforming Rte 4 Rte σ ioni (Ω 1 m 1 ) Rte resistive swithing ehviour ws oserve, whih inites tht the VHN-se evies work with nnosle eletroes. We note tht the physil ogeny of ommon ioni n eletroni hnnel s presume in the originl moel pulishe y Strukov et l. 40 n violtion of the Lnuer priniple, mong others, hve reently le to sientifi ispute 41,42. With the sptilly seprte ioni n eletroni nnohnnels foun in our SDC:STO evies, we hve experimentlly proven for the first time tht resistive swithes n inee e moelle y seprte ioni n eletroni hnnels 43. We lso note tht the high ensity (B2 inh 2 ) VHN strutures in this work voi egrtion prolems of ense, nnosle fetures, whih will e require for high ensity memories. Suh nnosle fetures forme from plin oxie films will require ion or eletron em milling steps whih re 1.5 Temperture (K) Rte 2 Rte 3 Rte 4 Rte 4 1,000/T (K 1 ) Figure 7 Eletroni n ioni trnsport properties of VHN eposite from ifferent film growth rtes. () Eletroforming-free resistive swithing properties of SDC:STO VHN films epening on full with t hlf mximum (FWHM) vlues in o-roking urves; (re squre); Rte 2 (re irle); Rte 3 (turquoise tringle); Rte 4 (turquoise hexgon). () Resistne vlues of the pristine sttes of the evie with SDC:STO VHN films eposite from ifferent growth rtes (re voltge: 0.2 V). Error rs re provie s s.. () Temperture-epenene of ioni onutivity (s ioni ) for SDC:STO VHN films eposite from ifferent growth rtes. (,e) Resistne vrition with repete eletril yles (with pplie voltges of 5 n þ 5 V for swithing n re voltge of 0.3 V) of SDC:STO VHN film evies with ifferent growth rtes. 450 no yes prolemti sine these proesses le to surfe oxygen efets n ssoite unontrolle eletroni onution 44. There re however limittions of the nnoomposite moel system stuie in this work for prtil ReRAM pplitions. First, the pulse lser eposition proess we use here is not in line/fully omptile with urrent integrte semionutor mnufturing. In this ontext, epitxil oxies n nowys e grown y slle, inustril growth routes suh s retive o-evportion 45. The nnoomposite films of this stuy oul e grown in similr wy. Also, our evies hve the potentil to e integrte into stte-of-the-rt silion tehnology sine growth of epitxil oxies n nnoomposite oxies on silion is now well-estlishe 46,47. Seon, reltively high voltges n urrents were use in this experimentl set-up for resistive swithing. Thus, onsierle power onsumption is require for evie opertion. Thir, the enurne we hieve is somewht exeeing yles, whih is elow the reor 2 yles reporte efore 48. On the other hn, the eletroforming-free swithing ehviour of our evies with etter ontrol over the uilt-in nnohnnels promises spe for improve evie performne. For exmple, the use of integrte trnsistors lose to the swithing evie to ontrol the urrent in the LRS (ref. 49) is one wy to hieve higher enurne n vriility. Further improvement strtegies shoul inlue oping of eh nnoomposite omponent, n tuning of the nnoomposite mterils n eletroes llowing seprte ioni n eletroni hnnel formtion. In ition, the nnoolumn withs, whih re ontrolle y the film growth rtes, nee to e lrger thn 17 nm for the evies to e eletroforming-free (Fig. 7, Rtes 1 n 2). Conerning the slility, swithing on the 20 nm sle using -AFM on nnoolumn is fesile, suggesting tht VHN-se evies work with nnosle eletroes (Supplementry Fig. 13). However, the reporte nnoolumn geometry n potentilly result in lrge evie to evie vrine (ue to eletroes prtilly overing nnoolumn). Therefore, enhnement of the nnoomposite film rystllinity is key-spet for ppliility. By inresing the egree of rystllinity, eletroforming-free properties n e hieve using smller nnoolumn with to potentilly further reue the evie sle without prouing lrge evie to evie vrine. Finlly, the use of the seprte ioni n eletroni nnohnnel strutures emonstrte here oul hve mny enefits in other ionotronis res, for exmple: The sptil seprtion etween onutne hnnels for ifferent speies is in goo greement with the lssil Hogkin Huxley Moel 50 for the simultion of iologil neurons (for exmple, physilly seprte potssium n soium ion hnnels). Here the two sptilly seprte hnnels, nmely the ioni n eletroni nnohnnels, respetively, emulte sptilly seprte hnnels of io-neurons. Suh n nlogy is not foun in onventionl memristive systems (where the ioni n eletroni pth re lolly inistinguishle) mking the sptilly seprte vertil hnnel struture moel system for rtifiil ognitive systems se on soli stte ionotronis. For ioni gting for trnsistors or memory pplitions, plin soli ioni films o not trnsfer ions suffiiently rpily ut the strutures stuie here hve orers of mgnitue higher ioni onution 18. Furthermore, there re severl potentil vntges of soli ioni memory evies over liqui ionilly gte oxie memory evies whih re eing wiely reserhe For thoes in fuel ells, mixe onutors re require ut it is very iffiult to hve suffiient ioni n eletroni onution elow 500 C. The seprte hnnel strutures hve overome these limittions y inuing enhnements in oth hnnels, ontrolle y reful mterils seletion. In 8 NATURE COMMUNICATIONS 7:12373 DOI: /nomms

9 NATURE COMMUNICATIONS DOI: /nomms12373 ARTICLE ition, one n preisely tune the ion onutivity y justing the growth rte (Fig. 7). Methos Film frition. Nnoomposite film growth ws evelope on the sis of tht of ref.18. Films were grown on 0.5 wt.% N-ope SrTiO 3 (001) single-rystlline sustrtes y pulse lser eposition with KrF lser (l ¼ 248 nm) with fluene of J m 2 n repetition rte of 1 10 Hz. A polyrystlline 20 t.% SDC trget, polyrystlline STO trget n polyrystlline trgets ontining SDC (Sm 3 þ onentrtions: 0, 10, 20 n 30 t.%) n STO of 50:50 molr rtio were use for plin SDC films, plin STO films n SDC:STO VHN films, respetively. During eposition, the sustrte temperture ws 825 C. Deposition ws kept in n O 2 tmosphere of 0.2 mr. The smples were post-nnele t 700 C for 1 h uner 900 mr O 2. We eposite irulr Pt eletroes y DC-mgnetron sputtering onto the film surfe with show msks for eletril mesurements. Chrteriztion. The phse n the rystlline qulity of thin films were investigte y o-2y n symmetri XRD on PANlytil Empyren highresolution X-ry iffrtometer using Cu-K rition (l ¼ Å). o-roking urves were otine y mesuring iffrte em intensities roun the SDC (002) s funtion of the ngle etween inient X-rys n smple surfe (o). For investigting in-plne orienttion, j sns were otine y 360 in-plne smple rottion roun (111) peks of the films n sustrtes. RSMs were ollete out the STO (-203). o-2y iffrtion peks n RSM peks were use to lulte lttie prmeters of the films. An FEI TitnTM G STEM with Cs proe orretor, operte t 200 kv ws use to evlute the struturl properties ross the interfe. Cross-setionl smples were prepre y stnr mnul grining n thinning of smples with finl ion-milling step (Gtn PIPS 691 preision ion polishing system). The pln-view TEM smple ws prepre y using fouse ion em with 3 kev G ions use s finl finishing step. The ross-setionl, n pln-view STEM imges re tken in long [100] n [001] STO sustrte iretion, respetively. To etermine film surfe morphology, AFM (Multimoe 8 SPM with Nnosope V ontroller) ws performe. To investigte lol onution t vertil interfes, we employe n Agilent 5500 snning proe mirosope. Commeril silion tips ote with pltinum/iriium were use for onutive AFM. We mesure the resistnes using two-proe sttion with hot plte n Keithley 2440 soure-meter. To mesure ioni trnsport hrteristis with temperture vrition, we use hot plte n n HP 4294A Preision Impene Anlyser. For ll mesurements, N-ope STO sustrtes were groune n the voltge is pplie to the Pt eletroes. Dt vilility. The uthors elre tht the t supporting the finings of this stuy re ville within the rtile n its Supplementry Informtion file. The numeril vlues of the t shown s the grphs re ville upon request from the orresponing uthor. Referenes 1. Wser, R. & Aono, M. Nnoionis-se resistive swithing memories. Nt. Mter. 6, (2007). 2. Klinin, S. V. & Splin, N. A. Funtionl ion efets in trnsition metl oxies. Siene 341, (2013). 3. Wser, R., Dittmnn, R., Stikov, G. & Szot, K. Reox-se resistive swithing memories nnoioni mehnisms, prospets, n hllenges. Av. Mter. 21, (2009). 4. Jeong, D. S., Shroeer, H. & Wser, R. Coexistene of ipolr n unipolr resistive swithing ehviors in Pt/TiO 2 /Pt stk. Eletrohem. Soli Stte Lett. 10, G51 G53 (2007). 5. Yng, J. J. et l. The mehnism of eletroforming of metl oxie memristive swithes. Nnotehnology 20, (2009). 6. Kim, D. C. et l. Eletril oservtions of filmentry onutions for the resistive memory swithing in NiO films. Appl. Phys. Lett. 88, (2006). 7. Szot, K., Speier, W., Bihlmyer, G. & Wser, R. Swithing the eletril resistne of iniviul islotions in single-rystlline SrTiO 3. Nt. Mter. 5, (2006). 8. Jnoush, M. et l. Role of oxygen vnies in Cr-ope SrTiO 3 for resistne-hnge memory. Av. Mter. 19, (2007). 9. Nin, Y. B., Strozier, J., Wu, N. J., Chen, X. & Igntiev, A. Eviene for n oxygen iffusion moel for the eletri pulse inue resistne hnge effet in trnsition-metl oxies. Phys. Rev. Lett. 98, (2007). 10. Yng, J. J. et l. Memristive swithing mehnism for metl/oxie/metl nnoevies. Nt. Nnotehnol. 3, (2008). 11. Shiuy, K., Dittmnn, R., Mi, S. & Wser, R. Impt of efet istriution on resistive swithing hrteristis of Sr 2 TiO 4 thin films. Av. Mter. 22, (2010). 12. Dernley, G., Stonehm, A. M. & Morgn, D. V. Eletril phenomen in morphous oxie films. Rep. Prog. Phys. 33, (1970). 13. Chunovskii, F. A., Oynets, L. L., Pergment, A. L. & Stefnovih, G. B. Eletroforming n swithing in oxies of trnsition metls: The role of metl insultor trnsition in the swithing mehnism. J. Soli Stte Chem. 122, (1996). 14. Ogw, A. et l. Eletroforming n resistne-swithing mehnism in mgnetite thin film. Appl. Phys. Lett. 91, (2007). 15. Yhiro, H., Eguhi, Y., Eguhi, K. & Ari, H. Oxygen ion onutivity of the eri-smrium oxie system with fluorite struture. J. Appl. Eletrohem. 18, (1988). 16. Anersson, D. A., Simk, S. I., Skoroumov, N. V., Arikosov, I. A. & Johnsson, B. Optimiztion of ioni onutivity in ope eri. Pro. Ntl A. Si. USA 103, (2006). 17. Eguhi, K., Setoguhi, T., Inoue, T. & Ari, H. Eletril properties of eri-se oxies n their pplition to soli oxie fuel ells. Soli Stte Ion. 52, (1992). 18. Yng, S. M. et l. Strongly enhne oxygen ion trnsport through smriumope CeO 2 nnopillrs in nnoomposite films. Nt. Commun. 6, 8588 (2015). 19. Ohno, T. et l. Short-term plstiity n long-term potentition mimike in single inorgni synpses. Nt. Mter. 10, (2011). 20. Lee, S. et l. Novel eletroforming-free nnosffol memristor with very high uniformity, tunility, n ensity. Av. Mter. 26, (2014). 21. Yu, S., Gun, X. & Wong, H.-S. P. Conution mehnism of TiN/HfO x /Pt resistive swithing memory: trp-ssiste tunneling moel. Appl. Phys. Lett. 99, (2011). 22. Jeong, D. S. & Hwng, C. S. Tunneling-ssiste Poole-Frenkel onution mehnism in HfO 2 thin films. J. Appl. Phys. 98, (2005). 23. Shottky, W. Hlleitertheorie er Sperrshiht. Nturwissenshften 26, 843 (1938). 24. Houng, M. P., Wng, Y. H. & Chng, W. J. Current trnsport mehnism in trppe oxies: A generlize trp-ssiste tunneling moel. J. Appl. Phys. 86, (1999). 25. Hsieh, Y.-H. et l. Lol onution t the BiFeO 3 -CoFe 2 O 4 tuulr oxie interfe. Av. Mter. 24, (2012). 26. Slluzzo, M. in Oxie Thin Films, Multilyers, n Nnoomposites (es Mele, P. et l.) Ch. 10 (Springer, 2015). 27. Spinelli, A., Torij, M. A., Liu, C., Jn, C. & Leighton, C. Eletroni trnsport in ope SrTiO 3 : Conution mehnisms n potentil pplitions. Phys. Rev. B 81, (2010). 28. Chen, Y. et l. Metlli n insulting interfes of morphous SrTiO 3 -se oxie heterostrutures. Nno Lett. 11, (2011). 29. Liu, Z. Q. et l. Origin of the two-imensionl eletron gs t LAlO 3 /SrTiO 3 interfes: The role of oxygen vnies n eletroni reonstrution. Phys. Rev. X 3, (2013). 30. Lee, S. W., Liu, Y., Heo, J. & Goron, R. G. Cretion n ontrol of two-imensionl eletron gs using Al-se morphous oxies/srtio 3 heterostrutures grown y tomi lyer eposition. Nno Lett. 12, (2012). 31. Wlrop, J. R., Grnt, R. W., Wng, Y. C. & Dvis, R. F. Metl Shottky rrier ontts to lph 6H-SiC. J. Appl. Phys. 72, (1992). 32. Prk, J. et l. Multiit opertion of TiO x -se ReRAM y Shottky rrier height engineering. IEEE Eletron Devie Lett. 32, (2011). 33. Wser, R. (es). Nnoeletronis n Informtion Tehnology-Avne Eletroni Mterils n Novel Devies (Wiley-VCH, 2003). 34. Kilner, J. A. & Steele, B. C. H. Nonstoihiometri Oxies (Aemi Press, 1981). 35. MMnus-Drisoll, J. L. Self-ssemle heteroepitxil oxie nnoomposite thin film strutures: esigning interfe-inue funtionlity in eletroni mterils. Av. Funt. Mter. 20, (2010). 36. Zhng, W., Rmesh, R., MMnus-Drisoll, J. L. & Wng, H. Multifuntionl, self-ssemle oxie nnoomposite thin films n evies. MRS Bull. 40, (2015). 37. Chen, A., Bi, Z., Ji, Q. X., MMnus-Drisoll, J. L. & Wng, H. Mirostruture, vertil strin ontrol n tunle funtionlities in selfssemle, vertilly ligne nnoomposite thin films. At Mter. 61, (2013). 38. Wouters, D. J., Wser, R. & Wuttig, M. Phse-hnge n reox-se resistive swithing memories. Pro. IEEE 103, (2015). 39. Cleroni, A., Sills, S., Cron, C., Froni, E. & Rmswmy, N. Engineering ReRAM for high-ensity pplitions. Miroeletron. Eng. 147, (2015). 40. Strukov, D. B., Snier, G. S., Stewrt, D. R. & Willims, R. S. The missing memristor foun. Nture 453, (2008). 41. Linn, E., Siemon, A., Wser, R. & Menzel, S. Appliility of well-estlishe memristive moels for simultions of resistive swithing evies. IEEE Trns. Ciruits Syst. I, Reg. Ppers 61, (2014). 42. Ventr, M. D. & Pershin, Y. V. On the physil properties of memristive, mempitive n meminutive systems. Nnotehnology 24, (2013). 43. Vlov, I. et l. Nnotteries in reox-se resistive swithes require extension of memristor theory. Nt. Commun. 4, 1771 (2013). NATURE COMMUNICATIONS 7:12373 DOI: /nomms

10 NATURE COMMUNICATIONS DOI: /nomms Sh, C.-T. Funmentls of Soli-Stte Eletronis (Worl Sientifi Pulishing Co. Pvt. Lt, 1991). 45. MMnus-Drisoll, J. L. et l. Strong pinning in very fst grown retive o-evporte GB 2 Cu 3 O 7 ote onutors. APL Mter. 2, (2014). 46. Bek, S.-H. & Eom, C.-B. Epitxil integrtion of perovskite-se multifuntionl oxies on silion. At Mter. 61, (2013). 47. Zhng, W. et l. Integrtion of self-ssemle vertilly ligne nnoomposite (L 0.7 Sr 0.3 MnO 3 ) 1 x :(ZnO) x thin films on silion sustrtes. ACS Appl. Mter. Interfes 5, (2013). 48. Lee, M.-J. et l. A fst, high-enurne n slle non-voltile memory evie me from symmetri T 2 O 5-x /TO 2-x ilyer strutures. Nt. Mter. 10, (2011). 49. Chen, Y.-S. et l. Roust high-resistne stte n improve enurne of HfO x resistive memory y suppression of urrent overshoot. IEEE Eletron Devie Lett. 32, (2011). 50. Hogkin, A. L. & Huxley, A. F. A quntittive esription of memrne urrent n its pplition to onution n exittion in nerve. J. Physiol. 117, (1952). 51. Misr, R., MCrthy, M. & Her, A. F. Eletri fiel gting with ioni liquis. Appl. Phys. Lett. 90, (2007). 52. Yng, Z., Zhou, Y. & Rmnthn, S. Stuies on room-temperture eletrifiel effet in ioni-liqui gte VO 2 three-terminl evies. J. Appl. Phys. 111, (2012). 53. Jeong, J. et l. Suppression of metl-insultor trnsition in VO 2 y eletri fiel inue oxygen vny formtion. Siene 339, (2013). 54. Wneky, A. K. et l. Fiel-effet trnsistors se on single nnowires of onuting polymers. J. Phys. Chem. C 111, (2007). Aknowlegements This work ws supporte y the Europen Reserh Counil (ERC) (Avne Investigtor grnt ERC-2009-AG NOVOX) n the Cmrige Commonwelth, Europen & Interntionl Trust. We further knowlege funing from ERC grnt InsituNANO, , (S.T. n S.H.) n the Engineering n Physil Sienes Reserh Counil (EPSRC), EP/P005152/1 (S.H.). Sni Ntionl Lortories is multi-progrm lortory mnge n operte y Sni Corportion, wholly owne susiiry of Lokhee Mrtin Corportion, for the US Deprtment of Energy s Ntionl Nuler Seurity Aministrtion uner ontrt DE-AC04-94AL The work t Los Almos ws supporte y the US Deprtment of Energy through the LDRD progrm n performe, in prt, t the Center for Integrte Nnotehnologies (CINT), US Deprtment of Energy, Offie of Bsi Energy Sienes user fility. M.F., J.J. n H.W. knowlege the support from the US Ntionl Siene Fountion, DMR (Texs A&M University) n DMR (Purue University). Author ontriutions S.C. n J.L.M.-D. oneive the ie. S.C. n S.L. frite the films. S.C. n C.Y. esigne n onute the experiments n interprete the t. S.C., C.Y. n A.K. performe -AFM. P.L., M.F., J.J. n H.W. rrie out the TEM works. S.T., Q.J. n S.H. ontriute to the interprettion of the mesurement results. J.L.M.-D. supervise the reserh. S.C., S.T., S.H. n J.L.M.-D. wrote the mnusript. All uthors isusse the results n implitions t ll stges, ontriute to the improvement of the mnusript text n hve given pprovl to the finl version of the mnusript. Aitionl informtion Supplementry Informtion ompnies this pper t ntureommunitions Competing finnil interests: The uthors elre no ompeting finnil interests. Reprints n permission informtion is ville online t reprintsnpermissions/ How to ite this rtile: Cho, S. et l. Self-ssemle oxie films with tilore nnosle ioni n eletroni hnnels for ontrolle resistive swithing. Nt. Commun. 7:12373 oi: /nomms12373 (2016). This work is liense uner Cretive Commons Attriution 4.0 Interntionl Liense. The imges or other thir prty mteril in this rtile re inlue in the rtile s Cretive Commons liense, unless inite otherwise in the reit line; if the mteril is not inlue uner the Cretive Commons liense, users will nee to otin permission from the liense holer to reproue the mteril. To view opy of this liense, visit r The Author(s) NATURE COMMUNICATIONS 7:12373 DOI: /nomms