Implementation of an electrically modifiable artificial synapse based on ferroelectric field-effect transistors using Al-doped HfO2 thin films

Abstract

Human brain-like synaptic behaviors of the ferroelectric field-effect transistors (FeFETs) were emulated by introducing the metal–ferroelectric–metal–insulator–semiconductor (MFMIS) gate stacks employing Al-doped HfO₂ (Al:HfO₂) ferroelectric thin films even at a low operation voltage. The synaptic plasticity of the MFMIS-FETs could be gradually modulated by the partial polarization characteristics of the Al:HfO₂ thin films, which were examined to be dependent on the applied pulse conditions. Based on the ferroelectric polarization switching dynamics of the Al:HfO₂ thin films, the proposed devices successfully emulate biological synaptic functions, including excitatory post-synaptic current (EPSC), paired-pulse facilitation (PPF), and spike timing-dependent plasticity (STDP). The channel conductance of the FeFETs could be controlled by partially switching the ferroelectric polarization of the Al:HfO₂ gate insulators by means of pulse-number and pulse-amplitude modulations. Furthermore, the 3 × 3 array integrated with the Al:HfO₂ MFMIS-FETs was also fabricated, in which electrically modifiable weighted-sum operation could be well verified in the 3 × 3 synapse array configuration.