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In this work, we investigated the effects of the crystal phase of ZrO 2 on charge trapping memtransistors (CTMTs) as synaptic devices for neural network applications. The ZrO 2 deposited through thermal (t-ZrO 2) atomic layer deposition (ALD) and plasma (p-ZrO 2) ALD were analyzed using an X-ray diffractometer, which indicated that the t-ZrO 2 consisted of pure cubic phase, whereas p-ZrO 2 consisted of both cubic and tetragonal phases. Through X-ray photoelectron spectroscopy analysis, we then constructed the energy band diagram of the gate stacks. The E C of t-and p-ZrO 2 with respect to tunneling and blocking Al 2 O 3 were 1.84 and 1.19 eV respectively. Because of the relatively large E C of t-ZrO 2 , the window of the flat band voltage (V FB) shift extracted from charge trapping capacitors was enlarged by 591.9 mV more than the one using p-ZrO 2 as the charge trapping layer. Retention was also improved by 10.4% after 10 5 s in the t-ZrO 2 case. Finally, we fabricated the CTMTs with the gate stack of the t-ZrO 2 case and demonstrated their characteristics as synaptic devices. With the optimization of pulse schemes, we reduced the nonlinear factors of depression (α d) and potentiation (α p) from −6.72 and 6.47 to 0.03 and 0.01 respectively, enlarged the ON/OFF ratio from 15.6 to 70.4 and increased the recognition accuracy from 27.6% to 86.5% simultaneously. INDEX TERMS Germanium, high-κ dielectrics, multilayer perceptron, neural network hardware, synaptic device, zirconium oxide.

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