Implementation of an Electrically Modifiable Artificial Synapse Based on Ferroelectric Field-Effect Transistor Using Al-doped HfO2 Thin Film

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 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 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 FeFET 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.