Artificial Synapses: Photoelectric Plasticity in Oxide Thin Film Transistors with Tunable Synaptic Functions (Adv. Electron. Mater. 12/2018)

Abstract

In article number https://doi.org/10.1002/aelm.201800556, Hong Wang, Ling Li and co‐workers successfully emulate versatile functions of a biological synapse based on indium–gallium–zinc oxide (IGZO) thin film transistors through a new design by combining photonic and electric stimuli. Meanwhile, the synaptic functions can be mediated by modulating the composition ratio of IGZO film. The work contributes to the development of neuromorphic electronics and the combination of photonics and electric has great prospects in optoelectronic applications.

Bio‐Inspired In‐Sensor Compression and Computing Based on Phototransistors

“…Under high‐intensity optical illumination, the ionization of lots of oxygen vacancies from deep neutral states to shallow doubly ionized donor states and the generation of a large number of photo‐generated charge carriers and protons from band‐to‐band excitation per unit time can be used to explain the occurrence of the above phenomenon, as shown in Figure S5a (Supporting information). [ 40,44 ] Moreover, the EPSC response is triggered and modulated by different V GS amplitudes spanning from 0.5 to 3 V (Figure 2b), thereby verifying that the EPSC of phototransistor can be adjusted by the V GS . Additionally, Figure 2c displays the corresponding EPSC responses for a single light pulse at 0.1 and 1 Hz (pulse widths of 5 and 0.5 s, respectively).…”

“…As the frequency decreases, the EPSC increases for longer presynaptic pulses during the UV light illumination, which can be attributed to the generation of a large number of photo‐excited electrons and holes, owing to the absorption of UV light. [ 40 ] Furthermore, when the UV light is removed, the photocurrent of the phototransistor decays slowly, due to the strong persistent photoconductivity (PPC) behavior of the IGZO film. [ 45 ] This PPC behavior is thought to originate from the slow recombination of electrons with ionized oxygen vacancies (Figure S5b, Supporting Information).…”

“…[ 39 ] As a proof of concept, indium‐gallium‐zinc‐oxide (IGZO) phototransistor is used to achieve in‐sensor compression and computing in this study. This is due to the fact that IGZO has been commercialized due to its excellent photoresponse, relatively high mobility, and high uniformity for large‐scale fabrication [ 40 ] Specifically, based on the optoelectronic switching and light‐tunable synaptic characteristics of IGZO TFTs, in‐sensor compression and RC network are implemented and verified, respectively. Next, these two systems are integrated to achieve the in‐sensor compression and computing.…”

Synaptic Plasticity Powering Long‐Afterglow Organic Light‐Emitting Transistors

“…We found that the atom ratio of indium in IGZO film strongly influences the device performance, including its threshold voltage (V Th ), its electron mobility and its light response behavior. [11] When irradiated for 5 s with a 312 nm UV light, IGZO films with low-indium-ratio (50%) did not show any obvious V Th shift and current change, whereas IGZO films with 65% and 80%-In content exhibited a negative shift of the V Th . However, before UV irradiation, highindium-ratio (80%) IGZO films showed a notable negative shift of V Th while the changes of the off-state current were modest.…”

“…This finding is in line with literature showing that the adjustment of memory behavior can be controlled by varying the exposure time to UV light. [11,14] Such a LTP behavior of the transistor provides the tool to power the light emitting material for a long-lasting emission.…”