Leakage Current Through the Ultra Thin Silicon Dioxide

Transcription

1 Aian Journal of Chemitry ol. No. 3 (009) Leakage Current Through the Ultra Thin Silicon Dioxide A. BAHA*. EME and. EZAZADEH Department of Phyic Faculty of Baic Science Univerity of Mazandaran P.O. Box Babolar ran alibahari@ymail.com A ignificant iue i.e. leakage of current through the gate oxide ha been conidered relevant to the ue of ultra thin (< - nm) pure oxide of ilicon in the next complementary metal oxide emiconductor (CMOS) device generation baed on the analytical Landauer-Buttiker method. The ratio of leakage of current through the ingle and double oxide wa alo etimated. The reult how that the double gate can reduce the leakage of current. Key Word: Thin film Nano tranitor CMOS Gate oxide dielectric Landaure-Buttiker method. NTODUCTON Silicon oxide ha received a tremendou attention in the lat year. t ha been an excellent gate dielectric of complementary metal oxide emiconductor (CMOS) device. Due to it' good tructure and amorphou interface between it and ilicon ubtrate and the other propertie uoted -4 numerou attempt to find a viable gate dielectric for CMOS have encountered two major difficultie: () increaing leakage current and () born penetration from poly ilicon gate electrode through ultra thin ilicon oxide. ndeed a further reduction of gate oxide thickne produce an exponential increae of direct tunneling leakage current poing a fundamental limit for further caling 5. However to date no other gate dielectric could replace to ilicon oxide and fill thi gap. Some reearcher have uggeted everal high-k dielectric for replacement of SiO 6. To overcome thi caling limit of ilicon oxide a gate inulator. But thee material can affect the carrier mobility through the channel of tranitor. n thi work we have tudied the uantized conductance of a ballitic uantum wire (QW) from contact reitance and diturbing the current flow. By uing the direct tranmiion probability of each probe contact and Landaure-Buttiker formalim a olution to overcome the caling limit of ilicon oxide a gate dielectric i it' ubtitution by double gate inulator. Becaue double gate can reduce the leakage current then ingle gate and thu appear to be promiing candidate for future CMOS generation. Theory: eferring to previou work 7 and the current literature 8 the future of CMOS integration reuire improvement of the gate dielectric material. n thi Department of Chemitry Payame Nour Univerity of Sari Sari ran.

2 400 Bahari et al. Aian J. Chem. work we ued ample geometry in Fig. for four terminal reitance meaurement on a QW with Ohmic contact in interface between electrode and channel. With uch geometrie the QW in particularity uantum point contact (QPC) i produce by tuning the gate voltage to negative value uch that the electron ga underneath get depleted. Fig.. Sample geometry with 4 voltage probe n thi regime a further reduction of the gate voltage caue the lateral electric field and with it the lateral depletion zone around the gate increae we can thu tune the electronic width and change the number (j) of occupied mode of the QPC. n a imple picture one can imagine that at the abence of magnetic field the fraction of the electron trajectorie cloe to the wire edge i minimized and the conductance of uch QPC can be uantized in unit of je/h. n thi picture the QPC i connected to ource S and drain D via a tranition region by ballitic trictly one-dimenional QW and the QPC itelf by a barrier with tranmiion probability T a hown in Fig.. Fig.. A QPC a a tranition region between ource and drain (left) and it' idealized mode (right). Thi region i one-dimenional lead and the contriction i a barrier with tranmiion probability T EXPEMENTAL The Silicon ample (n-type 5 Ω cm cm cm) were cut out of wafer with mm thickne. Thee ample were introduced in uartz tube. The chematic of ample layout in Fig. 3 clearly how that one gate can be active gate (e.g. ) while two other gate grounded. n thi cae the operation mode around gate i.e. the

3 ol. No. 3 (009) Leakage Current Through the Ultra Thin Silicon Dioxide 40 left and right of gate erve a ource and drain. Now let u how a top view of ballitic uantum wire circuit (Fig. 3). The gate i poly ilicon and gate dielectric i the ultra thin ilicon oxide. t i aumed that each contact can aborb all incoming electron and ditribute the emitted electron eually among all out going model in which it can be filled up to the electrochemical potential of thi contact (µ) at zero temperature. We define T p T p > (T p T p ) a a direct tranmiion probability of contact p () into contact (p). Therefore the data of reference 9 and the current conervation law we can apply the Landaure-Buttiker formula a follow: where p ( T ) pµ p Tp µ p To the ample hown in Fig. 3 and or P Gp G e T h ( ) p p and p () () µ (3) e Fig. 3. Edge tate in ytem with 4 voltage probe ESULTS AND DSCUSSON t i believed 0 that there i a negative oxide can ilicon ubtrate and incoming oxygen hould penetrate through the oxide film. To make bond with ilicon atom at the interface likewie the electron here can percolate all the way to the oppoite edge a hown in Fig. 3. From the work of Buttiker a gate tripe extend acro thi region and change the number of occupied landau level that meaured with 4 voltage probe. By tuning biaing the gate the electron denity we can arrive at the point that the filling factor under the gate will be maller than outide the gated area. Then edge tate will get redirected at the gate. Now we denote N and M for filling factor in the ungated and gated region repectively baed on the Landaure- Buttiker rule we have

4 40 Bahari et al. Aian J. Chem. which yield to N N 0 D 0 N 0 N 0 0 D N 0 N G 0 0 N M N M N M M -N N N 4 M N 3 M M N 4 0 M (4) (5) M N M M N 3 4 M (6) 4 3 MG where G e /h. The main point i that the edge tate (and or carrier) can not be redirected completely at the gate. Some carrier can pa through the gate for ultra thin gate oxide below - nm thi leakage current (labeled by factor of ) i of importance and the above obtained reult hould be modified a follow: N N 0 D 0 N 0 N 0 0 D -N 0 N G 0 0 N M N ( M+ S) N ( M+ S) M -N N N 4 (7) So M + S N 3 M M + S N 4 0 M (8)

5 ol. No. 3 (009) Leakage Current Through the Ultra Thin Silicon Dioxide (M N) + S M M + S N 4 M S + N 3 M (9) Fig. 4. Sample geometry with double gate oxide f we conider a double gate dielectric a hown in Fig. 4 and olved the Landaure-Buttiker euation for uch thi ytem we then have: * M N 3 M M N M * 3 4 3MN N M M N (M N) M 3M N 3 G C M N 4 M * 3 3 (0) () which i a coneuence of charge conervatie and with µ C -*µ C µ d 0. The comparion of ingle and double gate dielectric reult that mentioned above the carrier penetration through the double gate i lower than that for a ingle gate dielectric becaue the carrier encountered to two barrier in double gate.

6 404 Bahari et al. Aian J. Chem. Concluion n thi work the double oxide gate dielectric ha been invetigated in detail with the Landaure-Buttiker euation. Double oxide gate can reduce leakage of current more than that ingle oxide gate. We thu ugget double gate oxide to replace ingle gate dielectric for the future of CMOS generation 0-8. ACKNOWLEDGEMENT Thi work i upported with a grant from the Univerity of Mazandaran Babolar ran. EFEENCES. A. Bahari P. Morgen K. Pederen and Z.S. Li J. ac. Sci. Technol. B 4 9 (006)...J.. Baumvol E.P. Guev F.C. Stedile F.L. Freire M.L. Green and D. Braen Appl. Phy. Lett (998). 3. A. Bahari P. Morgen K. Pederen and Z.S. Li Newletter 9 (005). 4. T. Bieniek A. Wojtkiewicz L. Lukaiak and.b. Beck J. Wide Bandgap Mater. 8 0 (00). 5. T. Heinzel Meocopic Electronic in Solid State Nanotructure Weinheim Wiley-CH (003). 6..J.. Baumvol Sci. ep. 36 (999). 7. A. Bahari P. Morgen K. Pederen and Z.S. Li J.ac. Sci. Technol. B 4 9 (006). 8. M. Pourfath E. Ungerboeck A. Gehring B.H. Cheong W.J. Park H. Koina and S. Selberher Micro. Eng (005). 9. arxiv:cond-mat/ v 6 Jun (005) Magnetotranport in the preence of a longitudinal barrier: multiple uantum. 0..J. Haug J. Kucera P. Streda and K. Klitzing Phy. ev. B (989).. M. Buttiker Nature (997).. A. Bahari N. Mirnia and A. Pahlavan World Appl. Sci. J. 4 6 (008). 3. K. Navi. Zabihi M. Haghparat and T. Nikobin World Appl. Sci. J (008). 4. B. Bahmani-Firouzi E. Jamhidpour and T. Niknam World Appl. Sci. J (008). 5. K. Navi. Foroutan B. Mazloomnejad Sh. Bahrololoumi O. Hahemipour and M. Haghparat World Appl. Sci. J. 4 4 (008). 6.. Aigbedion World Appl. Sci. J. 77 (007). 7. M.M. Abd El-aheem World Appl. Sci. J. 04 (007). 8. P. Aadi and K. Navi World Appl. Sci. J. 34 (007). (eceived: 7 June 008; Accepted: 8 December 008) AJC-7070