Ferroelectric neuron integrated circuits using SrBi₂Ta₂O₉-gate FET's and CMOS Schmitt-Trigger oscillators

A pulse frequency modulation (PFM) type ferroelectric neuron circuit composed of a metal-ferroelectric-semiconductor field effect transistor (MFSFET) and a CMOS Schmitt-trigger oscillator was fabricated on a SOI structure, in which SrBi₂Ta₂O₉ (SBT) was used as a ferroelectric gate material of the FET. It was found that the fabricated MFSFET showed a relatively good I_D-V_G (drain current versus gate voltage) characteristic with a hysteresis loop due to ferroelectricity of the SBT film and that it acted as a synapse device with adaptive-learning function. It was also found that the output pulse height of the circuit was as high as the power supply voltage and that output pulse frequency was changed as the number of applied input pulses increased.