The practical application of optoelectronic artificial synapses in neuromorphic visual systems is still hindered by their limited functionality, reliability and the challenge of mass production. ...Here, an electro-photo-sensitive synapse based on a highly reliable amorphous InGaZnO thin-film transistor is demonstrated. Not only does the synapse respond to electrical voltage spikes due to charge trapping/detrapping, but also the weight is modified directly by persistent photocurrent effects under UV-light stimulation. Representative forms of synaptic plasticity, including inhibitory and excitatory postsynaptic currents, frequency-dependent characteristics, short-term to long-term plasticity transitions, and summation effects, are successfully demonstrated. In particular, optoelectronic synergetic modulation leads to reconfigurable excitatory and inhibitory synaptic behaviors, which provides a promising way to achieve the homeostatic regulation of synaptic weights. Moreover, the analogue channel conductance with 100 states is used as the weight update rule to perform MNIST handwritten digit recognition, using system-level LeNet-5 convolutional neural network simulations. The network shows a high recognition accuracy of 95.99% and good tolerance to noisy input patterns. This study highlights the commercial potential of mature optoelectronic InGaZnO transistor technology in edge neuromorphic systems.
An electro-photo-sensitive synapse based on a highly reliable InGaZnO thin-film transistor is demonstrated to mimic synaptic functions and pattern-recognition functions.
This paper analyzes the abnormal degradation induced by hydrogen annealing. Although device performance is enhanced after hydrogen annealing, an abnormal hump is observed in transfer characteristics ...(<inline-formula> <tex-math notation="LaTeX">{I}_{D} - {V}_{G} </tex-math></inline-formula>) under positive bias temperature stress (PBTS). Threshold voltage shift (<inline-formula> <tex-math notation="LaTeX">\Delta \text{V}_{\text {TH2}} </tex-math></inline-formula>) in this hump region increases with increasing stress voltage and temperature. Additionally, <inline-formula> <tex-math notation="LaTeX">\Delta \text{V}_{\text {TH2}} </tex-math></inline-formula> is independent of the channel width. A novel hydrogen rupture-diffusion model is proposed to explain the degradation. COMSOL simulation and <inline-formula> <tex-math notation="LaTeX">{C} - {V} </tex-math></inline-formula> measurement are utilized to clarify the precise degradation position. Moreover, variable S/D spacing (<inline-formula> <tex-math notation="LaTeX">\text{L}_{\text {SD}} </tex-math></inline-formula>) devices are designed to support the mechanism. Finally, ISE-TCAD software is carried out to verify the proposed model. Our results from electrical measurement suggest that hydrogen can cause additional instability, which shares a similar conclusion for those by using material analyzation and first-principle simulation.
The hump phenomenon along with a negative shift of threshold voltage emerging in the transfer characteristics of amorphous InGaZnO thin-film transistors under negative bias stress was investigated. ...Higher measurement temperature and larger bias voltage can induce more and faster hole injection, thus leading to the increased parasitic ON-state current and more negative shift of the threshold voltage. Nevertheless, the parasitic current is independent of the channel width, illustrating that the parasitic channel originates from the hole trapping near the IGZO edges along the channel length. Integrated Systems Engineering Technology Computer-aided Design simulation confirms that the electric field near the IGZO edge is relatively dense, and the direction is more conducive for the holes in IGZO to inject into passivation (PV), to gate insulator (GI), or at PV/GI interface.
The effects of mechanical tensile and compressive stress on dual‐gate amorphous InGaZnO thin‐film transistors (a‐IGZO TFTs) on a flexible substrate were investigated. Both the tensile and compressive ...stresses led to increases in free electrons and deep states in a‐IGZO. Strong tensile stress tends to form more deep defects than compressive stress, resulting in severe deterioration in performance. Small compressive stress seems to repair defects in the relatively poor quality etch‐stop layer (ESL), resulting in increased mobility in the top‐gate‐controlled performance.
The effects of mechanical stress on dual‐gate amorphous InGaZnO thin‐film transistors on a flexible substrate were investigated. Both the tensile and compressive stresses led to increases in free electrons and deep states in a‐IGZO. Strong tensile stress tends to form more deep defects, while small compressive stress seems to repair defects in the relatively poor quality etch‐stop layer.
This letter investigates flexible polycrystalline silicon thin film transistor performance variation due to different buffer layer thicknesses. In flexible electronics, thermal expansion stress ...during device fabrication is inevitable. A thicker SiO 2 buffer demonstrates better endurance to thermal expansion stress from the polyimide substrate during device annealing. However, if the SiO 2 buffer thickness is above a critical point, its weak heat dissipation capability causes the optimal ELA crystallization condition to shift. A thermal expansion stress simulation and TEM photos were utilized to verify performance variation. Furthermore, a similar trend was observed in electrical characteristics after negative bias temperature instability.
This letter analyzes performance and reliability of inverted staggered type amorphous indium-gallium-zinc oxide devices in a moist environment with H 2 O molecules in the passivation layer. There is ...a negative threshold voltage shift (Δ Vth) in the saturation region (VD = 10 V), which increases with decreasing channel length. We propose that this is explained by the drain-induced barrier lowering that is due to the H 2 O molecules. Moreover, a hydrogen bonding model under bias stress is also proposed, in contrast to the conventional H 2 O doping model. Recovery behavior after bias stress and ac operation were utilized to distinguish the difference between these models.
This paper systematically studies high-current-induced effects, hot-carrier effects, and self-heating effects in flexible low-temperature polycrystalline-silicon thin-film transistors fabricated on ...polyimide. By utilizing I-V and various-frequency C-V measurements, the exact location of defects generated by the self-heating effects can be clarified. The degradation mechanism is found to originate from asymmetric negative-bias temperature instability. After clarifying this mechanism, the self-heating effects were shown to be alleviated by manipulating the fabrication of the buffer layer, thereby improving heat dissipation capabilities.
In this letter, we investigated the gate insulator morphology affecting on the electric characteristic variation for organic thin-film transistors (OTFTs). From the transfer characteristics, there is ...a result with leakage current when the gate voltage is lower than the threshold voltage, which is due to the gate insulator thickness variation. Furthermore, regardless of whether the OTFT is operated under positive or negative bias stress, the more severe degradation happened in the hump region of transfer characteristics. Because a thinner gate insulator causes a high electric field, more charges are trapped in a gate dielectric stack.
In this letter, we propose a charge trapping technique to enhance passivated emitter rear contact solar cell efficiency without changing the fabrication process. We trap the charge by applying ...voltage to the rear contact between the SiNx passivation layer and Si substrate with special metal screen printing. Furthermore, different charge voltages were applied for IV curve, fill factor, efficiency, and series resistance comparisons. The IV curve was measured with white light, with results showing that the fill factor and efficiency increase and series resistance decrease with an increase in charge voltage. Finally, a model was proposed to explain the charge trapping effect in the passivation layer.
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