Symetrix Corporation Background

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Jonah Webb
5 years ago
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1 Symetrix Corporation Background Symetrix has strong history as IP provider > 25 years of development >200 U.S. and foreign patents. > $70M in research revenues, royalties and other income from development. Symetrix has licensed various technologies to eleven separate companies. Several of these technologies are in high volume production, most notably FeRAM at Panasonic. 1

2 Basic Idea of CeRAM Game Changer No Filaments Control of material properties and proper device architecture are fundamental to this new paradigm. Evidence? No filament formation. (No electroforming) The CeRAM resistor is designed to exploit materials properties, surface properties, switching mechanism (endurance) and memory mechanism (retention). Optimizing CeRAM is a different science than building the perfect filament. 2

3 Baseline The device is like a diode (varistor) to start with: Surface TRANSITION OXIDE Surface The surfaces are defect-rich with oxygen vacancies, transition metal excess, grain boundaries And a schottky barier!! 3

4 Baseline ReRAM Surface TRANSITION OXIDE (TMO) Surface 60 nm CeRAM CONDUCTIVE TMO T M O CONDUCTIVE TMO 10 nm Active Region 4

5 Why the Layers? Eliminate space charge at the interface Doping of TMO to make it conductive as-deposited (valence stabilization) Differential Doping to create active region that is switchable and repeatable ( pure phase transition) Isolate and thin the active region where the electronic switch property can be used exclusively----what electronic switching property? (Next slide) 5

6 IV Characteristics - Device Physics I = G D V? A I = G B V? BALLISTIC TRANSPORT V RESET I = G OFF V ~ 0 V SET B G D = DIFFUSIVE TRANSPORT DRUDE G B = BALLISTIC TRANSPORT DUE TO e-e CHARGE GAP CLOSING IN THE TRANSITION ION 3d ORBITALS G OFF = NO TRANSPORT IN INSULATING PHASE CONTROLLED BY e-e REPULSION IN 3d ORBITALS 6

7 Underlying Physical Mechanism? A V RESET V SET Is a quantum phase transition A Mott, charge transfer (CT) but not Anderson Extended band gap is of no consequence here Only localized electron matters (in the atom) Extremely high speed 80 femtoseconds 7

8 Underlying Physical Mechanism B? BALLISTIC TRANSPORT B V READ V RESET V SET Needs to be thermionic emission only to be sharp and cohesive so that it matches the charge gap energy (no fluctuations) 8

9 Mott Insulators MOTT TYPE E d n+1 U = U C E F U = 0 d n E F P d n-1 P INSULATOR DOS(E) DOS(E) 9

10 Mott Insulators CHARGE TRANSFER MOTT INSULATOR E d n+1 Δ E F U = 0 d n E F P P d n-1 INSULATOR DOS(E) DOS(E) 10

11 DOS(E) Charge Transfer M Mott Insulator E d n+1 Δ P E F d n-1 INSULATOR 11

12 IV Characteristics - Device Physics? A I = G B V? V RESET V SET A FROM TO INSULATOR PHASE TRANSITION B B FROM INSULATOR TO PHASE TRANSITION 12

13 The Switch The density of states modulates the screening length λ TF = ε 0 / e 2 DOS(E F ) The screening length modulates the current J 1 / λ TF Metal Side THE SWITCH IS HERE + (+) ELECTRON SEA (-) 13

14 Screening E F DOS Valence electrons screen the transition metal atom (ion) Narrows the potential well v(x) Releases localized electron closes the gap 14

15 Screening INSULATOR CHARGE GAP V(X) V Releases localized electron. Metal. Captures and localizes Electron repulsive u Opens the gap. Insulator. 15

16 Disproportionation A single atom can have oxidation and reduction reaction at the same time GAP = I A I = ionization energy A = e - AFFINITY d 9 U > 0 For Nickel (Oxide) ---- d 8 splits Into d 7 and d 9 d 7 16

17 Switching SPEED OF PHASE TRANSITION IN FEMTOSECONDS Active Region ELECTRON DRIFT VELOCITY IN NANOSECONDS C(((( (+) ONT ACT (-) Electron deficient at reset n(x) = n(critical) This causes U to appear 17

18 KEY POINTS The robustness of device switching requires control of the nickel ion oxidation number, specifically the suppression of Ni +4 and Ni 0 species that inhibit the pure Mott transition: 2Ni +2 Ni +1 + Ni +3 This is achieved with ligand doping, specifically CO -. Co - doping stabilizes the CeRAM resistive element at Ni +2 and the NiO film is conductive as-deposited. There is no rupturing and reformation of filaments, there is no oxygen diffusion (Memristor), only a pure Mott (charge transfer) phase transition 18

19 Technology Highlights Low temperature processing ~400c Robust retention at c - proved Reading at 0.2 volts times proved Read memory widens with device scaling Variability reduced due to clean surfaces and isolated active region proved Results demonstrated on 0.8µ devices only. Smaller feature sizes have been recently enabled under a program with Univesity of Texas at Dallas. 19

20 CeRAM STATUS THEORY: Confirmed with empirical results DONE MATERIALS: Doping any TMO with any extrinsic ligand PATENTED PROCESS: Create and isolate thin (5 nm) active region by simple spin-on or ALD PATENT FILED ARCHITECTURE: Array only (no pass gate) 3-D (STACKING) With only silicon friendly materials IN PROCESS FPGA Architecture PATENT FILED PATENTED 20

21 Implications A NEW DEVICE AND THEORETICAL PARADIGM HAS BEEN DEVELOPED FOR RESISTIVE SWITCHING MEMORIES, ONE THAT: Eliminates the oxygen diffusion effect (basis of memristor) to allow pure Mott-like transition. Reduces variability in key parameters (v set & v reset ) that has prevented ReRAM commercialization. Provides the robustness and repeatability required by future device scaling. Offers a path to 3d (stackable) memory architectures. May, in time, replace transistors as the fundamental switch in circuits. 21

Figure 3.1 (p. 141) Figure 3.2 (p. 142)

Figure 3.1 (p. 141) Figure 3.2 (p. 142) Figure 3.1 (p. 141) Allowed electronic-energy-state systems for two isolated materials. States marked with an X are filled; those unmarked are empty. System 1 is a qualitative representation of a metal;