Review of deep ultraviolet photodetector based on gallium oxide

Ultraviolet(UV) photodetectors(PDs) have drawn great attention in recent years due to their potential application in civil and military fields. Because of its ultrawide bandgap, low cost, strong radiation hardness, and high thermal and chemical stability with high visible-light transparency, Ga_2O_3 is regarded as the most promising candidate for UV detection.Furthermore, the bandgap of Ga_2O_3 is as high as 4.7–4.9 eV, directly corresponding to the solar-blind UV detection band with wavelength less than 280 nm. There is no need of doping in Ga_2O_3 to tune its bandgap, compared to AlGaN, MgZnO,etc, thereby avoiding alloy composition fluctuations and phase separation. At present, solar-blind Ga_2O_3 photodetectors based on single crystal or amorphous Ga_2O_3 are mainly focused on metal–semiconductor–metal and Schottky photodiodes.In this work, the recent achievements of Ga_2O_3 photodetectors are systematically reviewed. The characteristics and performances of different photodetector structures based on single crystal Ga_2O_3 and amorphous Ga_2O_3 thin film are analyzed and compared. Finally, the prospects of Ga_2O_3 UV photodetectors are forecast.

Low-cost dual-stage offset-cancelled sense amplifier with hybrid read reference generator for improved read performance of RRAM at advanced technology nodes

In this work,two process-variation-tolerant schemes for a current-mode sense amplifier(CSA)of RRAM were proposed:(1)hybrid read reference generator(HRRG)that tracks process-voltage-temperature(PVT)variations and solve the nonlinear issue of the RRAM cells;(2)a two-stage offset-cancelled current sense amplifier(TSOCC-SA)with only two capacitors achieves a double sensing margin and a high tolerance of device mismatch.The simulation results in 28 nm CMOS technology show that the HRRG can provide a read reference that tracks PVT variations and solves the nonlinear issue of the RRAM cells.The proposed TSOCC-SA can tolerate over 64% device mismatch.

Analysis of tail bits generation of multilevel storage in resistive switching memory

The tail bits of intermediate resistance states（IRSs） achieved in the SET process（IRSS） and the RESET process（IRSR） of conductive-bridge random-access memory were investigated. Two types of tail bits were observed, depending on the filament morphology after the SET/RESET operation.（i） Tail bits resulting from lateral diffusion of Cu ions introduced an abrupt increase of device resistance from IRS to ultrahigh-resistance state, which mainly happened in IRSS.（ii） Tail bits induced by the vertical diffusion of Cu ions showed a gradual shift of resistance toward lower value. Statistical results show that more than 95% of tail bits are generated in IRSS. To achieve a reliable IRS for multilevel cell（MLC） operation, it is desirable to program the IRS in RESET operation. The mechanism of tail bit generation that is disclosed here provides a clear guideline for the data retention optimization of MLC resistive random-access memory cells.

Highly uniform and nonlinear selection device based on trapezoidal band structure for high density nano- crossbar memory array

Crossbar array provides a cost-effective approach for achieving high-density integration of two-terminal functional devices. However, the ＂sneaking current problem＂, which can lead to read failure, is a severe challenge in crossbar arrays. To inhibit the sneaking current from unselected cells, the integration of individual selection devices is necessary. In this work, we report a novel TaOx-based selector exhibiting a trapezoidal band structure formed by tuning the concentration of defects in the oxide. Salient features such as a high current density （1 MA·cm^-2）, high selectivity （5 × 10^4）, low off-state current （-10 pA）, robust endurance （〉10^10）, self-compliance, and excellent uniformity were successfully achieved. The integrated one-selector one-resistor （1S1R） device exhibits high nonlinearity in the low resistance state （LRS）, which is quite effective in solving the sneaking current issue.

Modulating 3D memristor synapse by analog spiking pulses for bioinspired neuromorphic computing

Memristor based artificial synapses have demonstrated great potential for bioinspired neuromorphic computing in recent years. To emulate synaptic fimctions, such as short-term plasticity and long-term potentiation/depression, square pulses or combined complex pulse groups are applied on the device. However, in biological neuron systems, the action potentials are analog pulses with similar amplitudes. Furthermore, in biological systems, the intensity of the stimulus is coded into the frequency of action potentials to modulate the weight of synapses. Toward this programming method, we applied a series of analog spiking pulses with same peaks on Ru/TiOJTiN 3D memristor to emulate synaptic functions, such as long-term potentiation/depression and synaptic saturation. Moreover, we demonstrated the conductance change of the device under different stimulus frequencies of analog spiking pulses and described the statistical results of conductance change value, which shows that the device conductance has a larger change value under a higher spiking frequency with identical pulse number. These results show that the analog spiking pulses can well modulate the memristor-based synaptic weight and have a great potential for bioinspired computing in the future.