Synaptic Behaviors in Ferroelectric-Like Field-Effect Transistors with Ultrathin Amorphous HfO2 Film

Abstract

We demonstrate a non-volatile field-effect transistor (NVFET) with a 3-nm amorphous HfO2 dielectric that can simulate the synaptic functions under the difference and repetition of gate voltage (VG) pulses. Under 100 ns write/erase (W/E) pulse, a memory window greater than 0.56 V and cycling endurance above 106 are obtained. The storied information as short-term plasticity (STP) in the device has a spiking post-synaptic drain current (ID) that is a response to the VG input pulse and spontaneous decay of ID. A refractory period after the stimuli is observed, during which the ID hardly varies with the VG well-emulating the bio-synapse behavior. Short-term memory to long-term memory transition, paired-pulse facilitation, and post-tetanic potentiation are realized by adjusting the VG pulse waveform and number. The experimental results indicate that the amorphous HfO2 NVFET is a potential candidate for artificial bio-synapse applications.

Ferroelectric Devices for Intelligent Computing

“…Amorphous oxide-based FeFETs show good endurance characteristics but a severe degradation in the retention performance. Nonvolatile FETs with α-Al 2 O 3 show a stable MW without any degradation over 10 6 P/E cycles at ±3 V and 100 ns (Figure 7(c)) [51]. The trapping/detrapping effect is also a key factor that influences the MW of these devices.…”

“…Because amorphous materials lack domains or boundaries, the amorphous ferroelectric oxides mentioned above can be used for achieving nanoscale transistors exhibiting low device variation and nonvolatile storage function [46,47]. Amorphous materials that exhibit polarization switching include ZrO 2 [48], Al 2 O 3 [49,50], HfO 2 [51], La 2 O 3 [52], and TiO 2 [53], which are compatible with the conventional CMOS process and have been employed as high-κ gate dielectrics for logic transistors.…”

“…For embedded DRAM applications, program and erase speeds of approximately 10 ns can be achieved using a program voltage of 7.4 V and an erase voltage of −8.6 V, with an MW larger than 0.2 V [49]. An amorphous Al 2 O 3 nonvolatile FET can achieve a MW above 0.85 V under ±3 V at a pulse width of 100 ns under the program/erase (P/E) condition (Figure 7(b)) [51]. The P/E voltage can be further reduced to ±1.6 V, thus exhibiting the potential of the device for applications at a lower operation voltage compared to that of doped-HfO 2 FeFETs.…”

“…Moreover, FeFETs can simultaneously perform storage and processing functions; therefore, they can be used for artificial synapse applications involving spike neural networks (SNNs) [128] and convolutional neural network (CNNs) [51]. Many studies have investigated the writing methods of FeFETs as synapses in neural networks to achieve better performance.…”

Hafnium Oxide Nanostructured Thin Films: Electrophoretic Deposition Process and DUV Photolithography Patterning

“…Materials based on hafnium oxide (HfO 2 ) offer remarkable combinations of ferroelectricity, high dielectric permittivity, high energy barriers and high thermodynamic stability, which are of particular interest for next-generation high-κ gate dielectrics in microelectronics or nonvolatile memories, variable capacitors, biosensors, actuators and energy storage/harvesting devices [ 1 , 2 , 3 , 4 ]. These chemical and physical properties are known to be highly dependent on the presence of atomic defects and the amorphous nature or various crystal structures of HfO 2 , i.e., monoclinic (space group P 2 1 / c , the most stable at low temperature), tetragonal ( P 4 2 / nmc ), orthorhombic ( Pca 2 1 ) and cubic ( Fm 3 m ) [ 5 , 6 , 7 , 8 ]. Recently, metal oxide materials such as ZnO, TiO 2 and HfO 2 have emerged as alternatives to conventional organic photoresists and have been shown to be well suited to deep UV and extreme UV (DUV and EUV) photolithography processes [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 ].…”