Strain-based room-temperature non-volatile MoTe2 ferroelectric phase change transistor

Abstract

The primary mechanism of operation of almost all transistors today relies on electric-field effect in a semiconducting channel to tune its conductivity from the conducting 'on'-state to a nonconducting 'off'-state. As transistors continue to scale down to increase computational performance, physical limitations from nanoscale field-effect operation begin to cause undesirable current leakage that is detrimental to the continued advancement of computing 1,2 . Using a fundamentally different mechanism of operation, we show that through nanoscale strain engineering with thin films and ferroelectrics (FEs) the transition metal dichalcogenide (TMDC) MoTe2 can be reversibly switched with electric-field induced strain between the 1T'-MoTe2 (semimetallic) phase to a semiconducting MoTe2 phase in a field effect transistor geometry. This alternative mechanism for transistor switching sidesteps all the static and dynamic power consumption problems in conventional field-effect transistors (FETs) 3,4 . Using strain, we achieve large non-volatile changes in channel conductivity (Gon/Goff~10 7 vs. Gon/Goff~0.04 in the control device) at room temperature. Ferroelectric devices offer the potential to reach sub-ns nonvolatile strain switching at the attojoule/bit level 5-7 , having immediate applications in ultra-fast low-power non-volatile logic and memory 8 while also transforming the landscape of computational architectures since conventional power, speed, and volatility considerations for microelectronics may no longer exist.We design our device using single crystal oxide substrates of relaxor ferroelectric Pb(Mg1/3Nb2/3)0.71Ti0.29O3 (PMN-PT) as the gate dielectric (0.25-0.3 mm thickness). On top of this ferroelectric substrate we exfoliate 1T'-MoTe2 (13-70 nm) from a single crystal source, and pattern devices using Ni contact pads (Figure 1a,b). Exfoliation was performed in a humidity-controlled environment for increased adhesion. Depending on the contact material, stress from the deposited thin film strains the MoTe2 channel at the contact pads, analogous to the uniaxial strain techniques from strained silicon technology, widely adopted in industrial CMOS processes 9 . We find that contact metal stress and TMDC to substrate adhesion are both critically important for obtaining a functional device. During fabrication we are careful not to increase the temperature of the ferroelectric above 80° C, well below the Curie temperature of the ferroelectric at 135° C. Upon reaching the Curie temperature, the Device fabrication performed by W.H., A.S., T.P., and A.A.; Device characterization performed by W.H., A.A., and S.M.W.; Conductive atomic force microscopy performed by W.H., A.S., and S.M.W.; Strain gauge calibration performed by W.H. and S.M.W.; Topographic atomic force microscopy and optical contrast calibration performed by T.P.; Thin film stress measurements performed by C.W., A.A., W.H., and S.M.W.; Piezoresponse force microscopy performed by C.W.; Raman spectroscopy performed by A.A. and S.M.W.; Finite element analysis simul...

Reversible displacive transformation in MnTe polymorphic semiconductor

“…To realize such a hypothesis, we need further studies on the optimal memory cell structure, optimal electrode material, and optimal selector material for the MnTe memory layer. In addition, the MnTe film showing thermal-stress-induced polymorphic change should be a very attractive material for straintronics in which a phase transition induced by mechanical strain causes a change in electrical or optical properties 33,34 . Moreover, optically driven and fast martensitic transition has been recently theoretically and computationally illustrated in 2D materials, such as SnO and SnSe 35 .…”

A two-dimensional electron gas based on a 5s oxide with high room-temperature mobility and strain sensitivity

“…In addition, the static dielectric constant (~15) [53] of the BSO layer diminishes the electrostatic modulation of ferroelectric PMN-PT from ~30 C/cm 2 to a negligible value of ~5.3 nC/cm 2 at 4 kV/cm. Indeed, the electric-field-dependent RS curve resembles the asymmetric strain curve originating from 109° ferroelectric domain switching in (001)-oriented PMN-PT [50,52,54] owing to the non-volatile strain states of PMN-PT. As a result, such a heterostructure can work as a memory device of ultralow power consumption ( Fig.…”

2D Polarized Materials: Ferromagnetic, Ferrovalley, Ferroelectric Materials, and Related Heterostructures

“…demonstrated a ferroelectric strain FET memory device based on MoTe 2 /PMN‐PT structure. [ 183 ] The strain induced by electric field on PMN‐PT causes semiconductor‐semimetal phase change in MoTe 2 ( Figure a,b). The strain FET breaks the limitations of slow switch time, volatile, and SS issues and obtains a high on/off ratio (10 7 ) as well as a fast switch time.…”

“…a,b) Reproduced with permission. [ 183 ] Copyright 2019, Springer Nature. c,d) Output curves of FeS‐FET devices.…”