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Dynamic-load-enabled ultra-low power multiple-state RRAM devices.

Yang X, Chen IW - Sci Rep (2012)

Bottom Line: Bipolar resistance-switching materials allowing intermediate states of wide-varying resistance values hold the potential of drastically reduced power for non-volatile memory.This approach is entirely scalable and applicable to other bipolar RRAM with intermediate states.The projected power is 12 nW for a 100 × 100 nm(2) device and 500 pW for a 10 × 10 nm(2) device.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104-6272, USA.

ABSTRACT
Bipolar resistance-switching materials allowing intermediate states of wide-varying resistance values hold the potential of drastically reduced power for non-volatile memory. To exploit this potential, we have introduced into a nanometallic resistance-random-access-memory (RRAM) device an asymmetric dynamic load, which can reliably lower switching power by orders of magnitude. The dynamic load is highly resistive during on-switching allowing access to the highly resistive intermediate states; during off-switching the load vanishes to enable switching at low voltage. This approach is entirely scalable and applicable to other bipolar RRAM with intermediate states. The projected power is 12 nW for a 100 × 100 nm(2) device and 500 pW for a 10 × 10 nm(2) device. The dynamic range of the load can be increased to allow power to be further decreased by taking advantage of the exponential decay of wave-function in a newly discovered nanometallic random material, reaching possibly 1 pW for a 10×10 nm(2) nanometallic RRAM device.

No MeSH data available.


Related in: MedlinePlus

(a) Characteristic I–V curve of nanometallic bipolar RRAM: on-switching under negative voltage, off-switching under positive voltage.On-switching progresses in multiple steps, suggesting possibility of multi-bit memory. Cell size: 100×100 μm2. Upper left inset: schematic of device. Lower right inset: R–V curve. (b) R–V curves for various negative voltage limits from −12 V to −2 V. Plateau resistance increases as negative voltage limit reduces, causing off-switching voltage to decrease. (c) Off-switching power vs. negative voltage limit, −Vmax, showing ~60× power reduction as −Vmax decreases from 12 V to 2 V. Inset: I–V curve for Vmax = −2 V. (d) Simulated R–V curves under different −Vmax using parallel circuit model in Figure 2(b). Percentage in the bracket shows different F at plateau resistance. Simulation parameters: Vc*(V) = ±(1.2±0.2), Rl(Ω) = 330, rL/A(Ω) = 90, , where V is voltage in volt.
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f3: (a) Characteristic I–V curve of nanometallic bipolar RRAM: on-switching under negative voltage, off-switching under positive voltage.On-switching progresses in multiple steps, suggesting possibility of multi-bit memory. Cell size: 100×100 μm2. Upper left inset: schematic of device. Lower right inset: R–V curve. (b) R–V curves for various negative voltage limits from −12 V to −2 V. Plateau resistance increases as negative voltage limit reduces, causing off-switching voltage to decrease. (c) Off-switching power vs. negative voltage limit, −Vmax, showing ~60× power reduction as −Vmax decreases from 12 V to 2 V. Inset: I–V curve for Vmax = −2 V. (d) Simulated R–V curves under different −Vmax using parallel circuit model in Figure 2(b). Percentage in the bracket shows different F at plateau resistance. Simulation parameters: Vc*(V) = ±(1.2±0.2), Rl(Ω) = 330, rL/A(Ω) = 90, , where V is voltage in volt.

Mentions: Nanometallic thin films are insulator:metal atomic mixtures that exhibit thickness-dependent metal-insulator transitions, which can also be voltage-triggered allowing non-volatile RRAM. At small thickness less than the localization length of electrons in these random materials, metallic conduction is achieved at a metal composition well below the bulk percolation limit, which is a distinguishing feature of nanometallic materials82425. We fabricated nanometallic Si3N4:Cr films (10 nm thick) by co-sputtering Si3N4 and Cr onto unheated substrates using separate Si3N4 and Cr targets in a magnetron sputtering system at room temperature. As-fabricated devices (without forming) were nearly Ohmic-conducting. Under a voltage sweep, they exhibited bipolar switching behavior as shown in the I–V curve in Figure 3a obtained using the following voltage sweep: 0 V, to −12 V, to 10 V, to −12 V, and to 0 V. The initial sweep from 0 V to −12 V does not result in any sharp transition. Positive-voltage off-switching occurs at 8 V consuming ~250 mW, after that a non-Ohmic high resistance state (HRS), corresponding to F = 0, is reached. The HRS returns to the low resistance at −1 V, consuming ~30 μW during on-switching. In the above, power to operate the device was equated to the product of the applied voltage and current at the onset of switching. (This convention will be used throughout our work.) As shown in the inset of Figure 3a, from −12 V to 8 V the resistance (Rc+Rl) is flat, which will be referred to as plateau resistance to indicate no transition. This plateau-resistance state is actually one of the intermediate states with F <1. Note that the off-switching voltage in Figure 3a is relatively high signifying a relatively large Δ. This is caused by the very small Rc and large F, which was made possible according to Figure 2b by using a very large negative voltage limit (−12 V) during the negative sweep. Such high Δ and low Rc in turn raise P.


Dynamic-load-enabled ultra-low power multiple-state RRAM devices.

Yang X, Chen IW - Sci Rep (2012)

(a) Characteristic I–V curve of nanometallic bipolar RRAM: on-switching under negative voltage, off-switching under positive voltage.On-switching progresses in multiple steps, suggesting possibility of multi-bit memory. Cell size: 100×100 μm2. Upper left inset: schematic of device. Lower right inset: R–V curve. (b) R–V curves for various negative voltage limits from −12 V to −2 V. Plateau resistance increases as negative voltage limit reduces, causing off-switching voltage to decrease. (c) Off-switching power vs. negative voltage limit, −Vmax, showing ~60× power reduction as −Vmax decreases from 12 V to 2 V. Inset: I–V curve for Vmax = −2 V. (d) Simulated R–V curves under different −Vmax using parallel circuit model in Figure 2(b). Percentage in the bracket shows different F at plateau resistance. Simulation parameters: Vc*(V) = ±(1.2±0.2), Rl(Ω) = 330, rL/A(Ω) = 90, , where V is voltage in volt.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3473363&req=5

f3: (a) Characteristic I–V curve of nanometallic bipolar RRAM: on-switching under negative voltage, off-switching under positive voltage.On-switching progresses in multiple steps, suggesting possibility of multi-bit memory. Cell size: 100×100 μm2. Upper left inset: schematic of device. Lower right inset: R–V curve. (b) R–V curves for various negative voltage limits from −12 V to −2 V. Plateau resistance increases as negative voltage limit reduces, causing off-switching voltage to decrease. (c) Off-switching power vs. negative voltage limit, −Vmax, showing ~60× power reduction as −Vmax decreases from 12 V to 2 V. Inset: I–V curve for Vmax = −2 V. (d) Simulated R–V curves under different −Vmax using parallel circuit model in Figure 2(b). Percentage in the bracket shows different F at plateau resistance. Simulation parameters: Vc*(V) = ±(1.2±0.2), Rl(Ω) = 330, rL/A(Ω) = 90, , where V is voltage in volt.
Mentions: Nanometallic thin films are insulator:metal atomic mixtures that exhibit thickness-dependent metal-insulator transitions, which can also be voltage-triggered allowing non-volatile RRAM. At small thickness less than the localization length of electrons in these random materials, metallic conduction is achieved at a metal composition well below the bulk percolation limit, which is a distinguishing feature of nanometallic materials82425. We fabricated nanometallic Si3N4:Cr films (10 nm thick) by co-sputtering Si3N4 and Cr onto unheated substrates using separate Si3N4 and Cr targets in a magnetron sputtering system at room temperature. As-fabricated devices (without forming) were nearly Ohmic-conducting. Under a voltage sweep, they exhibited bipolar switching behavior as shown in the I–V curve in Figure 3a obtained using the following voltage sweep: 0 V, to −12 V, to 10 V, to −12 V, and to 0 V. The initial sweep from 0 V to −12 V does not result in any sharp transition. Positive-voltage off-switching occurs at 8 V consuming ~250 mW, after that a non-Ohmic high resistance state (HRS), corresponding to F = 0, is reached. The HRS returns to the low resistance at −1 V, consuming ~30 μW during on-switching. In the above, power to operate the device was equated to the product of the applied voltage and current at the onset of switching. (This convention will be used throughout our work.) As shown in the inset of Figure 3a, from −12 V to 8 V the resistance (Rc+Rl) is flat, which will be referred to as plateau resistance to indicate no transition. This plateau-resistance state is actually one of the intermediate states with F <1. Note that the off-switching voltage in Figure 3a is relatively high signifying a relatively large Δ. This is caused by the very small Rc and large F, which was made possible according to Figure 2b by using a very large negative voltage limit (−12 V) during the negative sweep. Such high Δ and low Rc in turn raise P.

Bottom Line: Bipolar resistance-switching materials allowing intermediate states of wide-varying resistance values hold the potential of drastically reduced power for non-volatile memory.This approach is entirely scalable and applicable to other bipolar RRAM with intermediate states.The projected power is 12 nW for a 100 × 100 nm(2) device and 500 pW for a 10 × 10 nm(2) device.

View Article: PubMed Central - PubMed

Affiliation: Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA 19104-6272, USA.

ABSTRACT
Bipolar resistance-switching materials allowing intermediate states of wide-varying resistance values hold the potential of drastically reduced power for non-volatile memory. To exploit this potential, we have introduced into a nanometallic resistance-random-access-memory (RRAM) device an asymmetric dynamic load, which can reliably lower switching power by orders of magnitude. The dynamic load is highly resistive during on-switching allowing access to the highly resistive intermediate states; during off-switching the load vanishes to enable switching at low voltage. This approach is entirely scalable and applicable to other bipolar RRAM with intermediate states. The projected power is 12 nW for a 100 × 100 nm(2) device and 500 pW for a 10 × 10 nm(2) device. The dynamic range of the load can be increased to allow power to be further decreased by taking advantage of the exponential decay of wave-function in a newly discovered nanometallic random material, reaching possibly 1 pW for a 10×10 nm(2) nanometallic RRAM device.

No MeSH data available.


Related in: MedlinePlus