A High‐Performance Ag/TiN/HfO_x/HfO_y/HfO_x/Pt Diffusive Memristor for Calibration‐Free True Random Number Generator

Abstract

True random number generators (TRNGs) that can generate unpredictable data by exploiting physical entropy sources are the main security primitive. Despite impressive demonstrations of TRNGs with various memories by exploiting their spatiotemporal variability, realizing efficient and reliable TRNGs without calibration remains a significant challenge. Diffusive memristors with rich stochastic switching behaviors offer an attractive alternative to designing efficient TRNGs, but they are still plagued by difficulties in improving device performance and inefficient circuit calibration. Here, the authors report a Ag/TiN/HfOx/HfOy/HfOx/Pt diffusive memristor with superior threshold switching characteristics, enabled by the good control of switching dynamics by introducing a TiN barrier and trilayer‐hafnia with different ion mobility and migrate barriers. The random integrate‐and‐fire behaviors of the memristor are exploited as excellent intrinsic entropy sources for random number generation with robustness to device variation and without extra calibration. Experimental measurements validate the highly stochastic, compact, self‐clocking TRNG design with a high throughput of ≈108 kb s‐1. The generated random bits have successfully passed all 15 National Institute of Standards and Technology randomness test benchmarks. This work demonstrates that high‐performance diffusive memristors can play an important role in hardware security electronics deployed in edge computing systems.

A review of memristor: material and structure design, device performance, applications and prospects

“…The on-off ratio is defined as the ratio between the currents in the high and low resistance states of the memristor. As shown in Figure 7(a) , Lu et al fabricated a Ag/TiN/HfO x /HfO y /HfO x /Pt memristor, and it had an ultra-high switching ratio of 10 10 [ 162 ]. We have fabricated a Pt/BFO/HfO 2 /TiN device by inserting a 2 nm BiFeO 3 layer, achieving a pulse endurance of 10 8 cycles ( Figure 7(b) ) [ 61 ].…”

“… (a) Repeatable 100 cycles of Ag/TiN/HfO x /HfO y /HfO x /TiN/Ag device under an I CC of 3 mA, indicating an extremely high ON/OFF ratio of over 10 10 . Reproduced with permission from [ 162 ], copyright 2022, Wiley. (b) Endurances of HfO 2 -based memristors before and after inserting the BFO layer.…”

Volatile threshold switching memristor: An emerging enabler in the AIoT era

“…3(b)). To limit the sneak current from the unselect or half-select memory element during both read and write operation, an ideal selector should have high non-linearity (on/off ratio) and ultra-low leak- Cu/Cu:HfO 2 /HfO 2 /Pt [85] 0.4 10 μA 1 pA 10 7 -50 ns/100 ns Unidirectional Cu/SiO 2 /Pt [21] 0.7 500 μA 10 pA 5 × 10 7 50 4 ms/1 ms Unidirectional Ag/ZrO 2 /Pt [175] 0.25 1 mA 100 pA 10 7 200 -Unidirectional Ag/SiTe/TiN [176] 0.6 100 μA 10 nA 10 4 10 5 5 μs/3 μs Unidirectional Ag/DDG/SiO 2 /Pt [83] 0.6 500 μA 1 pA 5 × 10 8 10 6 100 ns/1 μs Bidirectional Ag/HfO 2 /Pd [75] 0.15 1 mA 0.1 pA 10 10 10 8 75 ns/250 ns Unidirectional Ag/HfO 2 :N/Pt [173] 0.2 500 μA 1 pA 5 × 10 8 10 6 1.5 μs/5 μs Unidirectional Ag/MoS 2 /Au [32] 0.35 100 μA 100 pA 10 6 5 × 10 6 -Unidirectional Pt/Cu 2 O/Ag:Cu 2 O/Cu 2 O/Pt [177] 0.5 1 μA 1 nA 10 3 --Bidirectional Ag/TaO x /TaO y /TaO x /Ag [178] 0.15 1 mA 1 pA 10 9 10 6 75 ns/500 ns Bidirectional Ag nanodot/HfO 2 /Pt [76] 0.25 1 mA 1 pA 10 9 10 8 110 ns/240 ns Bidirectional AgTe 35% /TiN/TiO 2 /Pt [169] 0.4 100 μA 0.1 pA 10 9 10 8 10 ns/100 ns Unidirectional AgGeSe/Al 2 O 3 /Pt [81] 0.4 3 mA 0.1 pA 10 10 10 5 300 ns/30 μs Unidirectional Ag/TiN/HfO 2 /Pt [82] 0.2 100 μA 10 pA 10 7 10 5 28 ns/50 μs Unidirectional Pt/Ag:ZnO 2 /Pt [84] 0.7 1 mA 10 fA 10 11 10 6 38 ns/64 ns Unidirectional Ag/TiN/HfO x /HfO y /HfO x /Pt [86] 0.25 3 mA 0.1 pA 10 10 10 6 60 ns/500 ns Unidirectional Ge-Se [90] 1.4 450 μA 129 nA 10 3 10 8 2 ns Bidirectional Ge 58 Se 42 [91] 3.5 10 μA 100 pA 10 5 10 9 50 ns Bidirectional Ge-Se-N [92] 4 450 μA 2 nA 10 5 10 8 -Bidirectional Ge-Se-As [93] 2.5 10 mA 1 nA 10 7 5×10 5 -Bidirectional Ge-Se-Sb-N [94][95][96] 1.94 100 μA 10 pA 10 6 10 9 -Bidirectional GeTe 6 [97] 1.6 650 μA -10 5 600 5 ns Bidirectional Ge-As-Se-Te [98] 1 1 μA 200 pA 10 3 10 10 -Bidirectional Ge-As-Te-Si [99] 1.2 100 μA 1 μA 10 2 10 2 -Bidirectional Ge-As-Te-Si-Se [100,101] 2.2 420 μA 1.9 nA 10 5 10 10 50 ns Bidirectional Si-Te…”

“…Multilayer structure is another simple and effective method. In a study of back-end-of-the-line (BEOL) compatible selectors, Luo et al [85] inserted an undoped HfO 2 layer into a Cu/Cu:HfO 2 /Pt device. The tunneling layer reduced the leakage current by more than 5 orders of magnitude, which could greatly increase the array density.…”

SET Kinetics of Ag/HfO2-Based Diffusive Memristors under Various Counter-Electrode Materials

“…This is achieved through the formation of a thin (a few nm in diameter) and unstable filament, which spontaneously ruptures within a certain amount of time once the voltage bias is removed, causing the cell to restore the initial high resistance state [ 12 ]. Volatile ECM cells, hereinafter referred to as diffusive memristors (DMs), are useful for a variety of applications in data storage and neuromorphic computing areas, such as selector [ 11 ], artificial neuron [ 13 ], true random number generator [ 14 , 15 ], and short-term synapse [ 16 , 17 ].…”