Biologically-inspired learning device using three-terminal ferroelectric memristor

A simple synaptic device with a spike-timing-dependent synaptic plasticity (STDP) learning function is a key device that can realize a brain-like processor. STDP is a learning mechanism of synapses in mammalian brains [1]. A memristor [2, 3] is a promising candidate for synaptic devices. However, since the conventional memristor is a two-terminal electric element and the signal magnitude at learning exceeds the processing, it is difficult to realize STDP learning by simultaneously processing the signal. We proposed a unique three-terminal memristor using a ferroelectric thin film [4]. Its three-terminal device structure enables the STDP function without disturbing the signal processing between neurons (Fig. 1). This all oxide memristor (OxiM) has a ferroelectric gate field-effect transistor structure (Fig. 2). Since the polarization of Pb(Zr,Ti)O₃ film is changed by applying gate voltage (V_G), the channel conductance at the ZnO / Pr(Zr,Ti)O₃ interface can be modulated (Fig. 3). Memorized conductance can be maintained without fluctuation [4]. In addition, ferroelectric polarization can be modulated by changing the height and the width of the applied voltage pulse to the gate electrode. Fig. 4 shows the conduction change after applying pulse voltages.