Synaptic behavior of flexible IGZO TFTs with Al2O3 gate insulator by low temperature ALD

Flexible InGaZnO (IGZO) thin-film transistor (TFT) with Al
2
O
3
gate insulator (GI) which is deposited by low temperature (LT) atomic layer deposition (ALD) is proposed and its synaptic behavior and mechanical stability are demonstrated on a polyethylene terephthalate substrate. The change of threshold voltage under bending test is attributed to the generation of ionized oxygen vacancy resulting from the oxygen bond-breaking. In addition, the synaptic behavior is clearly observed and the convolutional neural network-based MNIST recognition rate of 87.2 % after 60,000 training is demonstrated by using the proposed IGZO TFTs. Stable synaptic behavior can be explained by the potentiation/depression pulse-dependent movement of hydrogens which the Al
2
O
3
GI contains during LT ALD. Furthermore, it is found that the synaptic weight can be controlled and optimized by changing the thickness of Al
2
O
3
GI.