Monolithic In2Se3–In2O3 heterojunction for multibit non-volatile memory and logic operations using optoelectronic inputs

Abstract

Stable ferroelectricity at room-temperature down to the monolayer limit, harnessed with strong sensitivity towards visible-to-near-infrared illumination in α-In2Se3, facilitates its potential as versatile building block for developing ultrathin multifunctional photonic integrated networks. Herein, we demonstrated a planar ferroelectric-semiconductor heterojunction (FeS-HJ) field-effect transistor (FET) fabricated out of α-In2Se3 and In2O3, where the ferroelectric-polarization state in α-In2Se3 is utilized to control the device characteristics. The robust in-plane (IP) polarization flipping triggered by out-of-plane (OOP) electrostatic field along with clear anticlockwise hysteresis loop were readily revealed by scanning Kelvin-probe force microscopy (KPFM) and electrical probing. The orthogonally tangled ferroelectric switching was used to manipulate the HJ channel conductance and thereby to realize non-volatile memory (NVM) states. Moreover, gate-tuneable diode-like characteristics and superior photoresponse in HJ compared to its individual constitutes were observed. Utilizing the concurrent ferro-photonic coupling, high bandwidth optical inputs further tailored the outputs into four distinguished current states induced by different polarization directions. Our results pave the way for developing advanced (opto) electronic devices with diverse signal modulation capability to realize next generation low-power neurocomputing, brain-inspired visionary systems, and on-chip optical communications.

Edge-Based Two-Dimensional α-In2Se3–MoS2 Ferroelectric Field Effect Device

“…Figure b shows the transfer characteristics of the device for different gate voltage sweep ranges for V D = 2 V. A progressively increasing clockwise hysteretic behavior (see Supporting Information) is observed with respect to the applied sweep range (inset of Figure b). Such clockwise transfer characteristics have been previously observed in 2D ferroelectric based back-gated FETs with thick dielectrics and was attributed to dipole switching in ferroelectric semiconductor FETs. ,− This concurrent ferroelectric modulation of α-In 2 Se 3 , can substantially affect the conductivity of the MoS 2 channel (up to ∼4 orders of current magnitude for an applied gate potential of −20 V), thereby realizing nonvolatile memory operation (note that the measured current values are significantly larger in the on state, i.e., ∼10 μA, in comparison with typical current levels for In 2 Se 3 -based FET devices having similar geometry, ,− which are in the nA–pA range, indicative for the negligible current flow through the In 2 Se 3 layer).…”

“…Figure a presents the measured current–voltage output characteristics of the FeFET following three different poling conditions, viz., unpoled and poled at ±90 V (measurements took place 2 min after the withdrawal of gate bias voltage to allow for discharge of induced electronic trapped charge and stabilization of the current level as will be discussed further below). Such relatively high switching voltages required for complete polarization switching are attributed to the 300 nm SiO 2 dielectrics that results in weaker induced vertical electric field across the device channel. , A significant modulation of the channel conductance is clearly observed due to the different poling conditions. In particular, following positive (negative) gate poling, in which the polarization in the underlying α-In 2 Se 3 points upward (downward) the MoS 2 , the conductivity of the channel decreases (increases) significantly, realizing two distinct stable conduction states, i.e., on and off states.…”

“…The ferroelectric polarization in 2D In 2 Se 3 and its subsequent control by gate voltage has been established in a previous study 29 where correlated PFM and KPFM data were utilized to establish a direct connection between the gate tuned surface potential and switchable polarization in In 2 Se 3 FETs. Such gate-induced ferroelectric switching can be utilized to modulate the electronic band structure of the FeFET 45 and consequently the optoelectronic characteristics of the adjacent MoS 2 semiconducting channel. To investigate such dipoleinduced nonvolatile device characteristics, electrostatic poling of the In 2 Se 3 was performed by applying a particular gate bias voltage pulse for a duration of 30 s followed by the withdrawal of the gate voltage and assessment of the current voltage characteristics of the heterojunction device.…”

“…Such relatively high switching voltages required for complete polarization switching are attributed to the 300 nm SiO 2 dielectrics that results in weaker induced vertical electric field across the device channel. 29,45 A significant modulation of the channel conductance is clearly observed due to the different poling conditions. In particular, following positive (negative) gate poling, in which the polarization in the underlying α-In 2 Se 3 points upward (downward) the MoS 2 , the conductivity of the channel decreases (increases) significantly, realizing two distinct stable conduction states, i.e., on and off states.…”

Graphene-In2Se3 van der Waals Heterojunction Neuristor for Optical In-Memory Bimodal Operation

“…3 Very recently, electrically controlled photocurrent modulation by polarization switching has been demonstrated for NVM, photodetection, and 2-bit logic devices. 30 Other studies showed light pulse induced domainboundary movement enabling "optical write−electrical erase" memory cells, 31 as well as optoelectronic synapses, 3,32−34 in 2D α-In 2 Se 3 .…”