A Scanning Microwave Impedance Microscopy Study of 𝜶-In2With3 Ferroelectric Semiconductor
Lin Wang, Han Chen, Mingfeng Chen, Yinfeng Long, Kai Liu, Kian Ping Loh
Abstract
Van der Waals ferroelectric semiconductors, which encompass both ferroelectricity and semiconductivity, have garnered intensive research interests for developing novel non-volatile functional devices. Previous studies focus on ferroelectricity characterization and device demonstration, with little attention paid to the fundamental electronic properties of these materials and their functional structures, which are essential for both device design and optimization. In this study, scanning microwave impedance microscopy (sMIM) is utilized to investigate the ferroelectric semiconductor of α-phase indium selenide (α-In2With3) and its synaptic field effect transistors. α-In2With3 nanoflakes of varying thicknesses are visualized through capacitive signal detection, whose responses are consistent with finite element simulations manifesting dependence on both flake thickness and its semiconductor property. sMIM spectroscopy performed on α-In2With3-based metal-oxide-semiconductor (MOS) structures reveals typical MOS capacitance-voltage characteristics, with additional hysteresis arising from the ferroelectric switching of α-In2With3. The local conductance state changes of synaptic α-In2With3 ferroelectric semiconductor transistors (FeSFET) in response to gate voltage stimuli are effectively detected by in situ sMIM, in good agreement with electrical device transport properties. This work deepens the understanding of ferroelectric semiconductor physics toward their practical device application.
Summary of the paper
This study employs scanning microwave impedance microscopy (sMIM) to investigate the electronic properties of the van der Waals ferroelectric semiconductor α−In2With3and its synaptic ferroelectric semiconductor field-effect transistors (FeSFETs).
Key findings include:
For α−In2With3nanoflakes, sMIM' s capacitive signal (sMIM-C) shows a quasi-inverse correlation with thickness below 100 nm (saturating beyond this) — consistent with finite element simulations, reflecting thickness-dependent carrier depletion and semiconductor properties.
sMIM spectroscopy on α−In2With3-based metal-oxide-semiconductor (MOS) structures reveals classic MOS capacitance-voltage (C-V) behavior, with additional hysteresis attributed to ferroelectric switching of α−In2With3.
In situ sMIM effectively detects local conductance state changes (low resistance state, LRS; high resistance state, HRS) in α−In2With3synaptic FeSFETs under gate voltage stimuli. The sMIM signals align well with device transport data, quantifying LRS/HRS conductivities and validating sMIM' s utility for non-invasive monitoring of synaptic states.
This work advances understanding of ferroelectric semiconductor physics and establishes sMIM as a powerful tool for optimizing α−In2With3-based neuromorphic devices.
In this article, the specific application scenarios and functions of scanning microwave impedance microscopy SMIM are as follows:
- Characterizing the thickness and semiconductor properties of α-In₂Se₃ nanosheets: sMIM capacitance signal (sMIM-C) was used to detect α-In₂Se₃ nanosheets with different thicknesses. It was found that the signal has a quasi-inverse relationship with the thickness below 100nm, and is saturated after exceeding 100nm. This result is consistent with the finite element simulation and reflects the thickness-dependent carrier depletion characteristics of the nanosheets and their semiconductor properties.
- Analyze the capacitance characteristics of α-In₂Se₃-based MOS structure：The α-In₂Se₃-based metal-oxide-semiconductor (MOS) structure was characterized by sMIM spectra. Typical MOS capacitance-voltage (C-V) characteristics were observed, and additional hysteresis was caused by the ferroelectric switching effect of α-In₂Se₃. At the same time, the bias peak corresponding to the ferroelectric switch was captured through the d (sMIM-C)/dV signal, clarifying the synergy between semiconductor characteristics and ferroelectric switching.
- In-situ monitoring of the conductance state of α-In₂Se₃ synaptic FeSFET: In-situ sMIM characterization of α-In₂Se₃ ferroelectric semiconductor field-effect transistor (FeSFET) clearly distinguishes the sMIM-C signal difference between the low resistance state (LRS) and the high resistance state (HRS). The signal changes are consistent with the device transport characteristics; combined with simulations, it is deduced that the LRS/HRS conductivities are approximately 10 S/m and 10 S/m respectively. 10⁻² S/m, enabling non-invasive and quantitative monitoring of the local conductance state of synaptic devices.
