skip to main content

Title: Enhanced electrodynamic gating in two-dimensional transistors using ferroelectric capping
Abstract

Two-dimensional (2D) materials such as semiconductors and ferroelectrics are promising for future energy-efficient logic devices because of their extraordinary electronic properties at atomic thickness. In this work, we investigated a van der Waals heterostructure composited of 2D semiconducting MoS2and 2D ferroelectric CuInP2S6(CIPS) and NiPS3. Instead of using 2D ferroelectrics as conventional gate dielectric layers, here we applied CIPS and NiPS3as a ferroelectric capping layer, and investigated a long-distance coupling effect with the gate upon the sandwiched 2D MoS2channels. Our experimental results showed an outstanding enhancement of the electrodynamic gating in 2D MoS2transistors, represented by a significant reduction of subthreshold swing at room temperature. This was due to the coupling-induced polarization of 2D ferroelectrics at 2D semiconductor surface which led to an effective and dynamic magnification of the gate capacitance. Meanwhile, the electrostatic gating was remained steady after adding the ferroelectric capping layer, providing ease and compatibility for further implementation with existing circuit and system design. Our work demonstrates the long-distance coupling effect of 2D ferroelectrics in a capping architecture, reveals its impacts from both electrodynamic and electrostatic perspectives, and expands the potential of 2D ferroelectrics to further improve the performance of energy-efficient nanoelectronics.

Authors:
; ; ; ; ; ; ; ; ; ;
Publication Date:
NSF-PAR ID:
10436931
Journal Name:
Nano Express
Volume:
4
Issue:
3
Page Range or eLocation-ID:
Article No. 035002
ISSN:
2632-959X
Publisher:
IOP Publishing
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Memristive systems offer biomimetic functions that are being actively explored for energy‐efficient neuromorphic circuits. In addition to providing ultimate geometric scaling limits, 2D semiconductors enable unique gate‐tunable responses including the recent realization of hybrid memristor and transistor devices known as memtransistors. In particular, monolayer MoS2memtransistors exhibit nonvolatile memristive switching where the resistance of each state is modulated by a gate terminal. Here, further control over the memtransistor neuromorphic response through the introduction of a second gate terminal is gained. The resulting dual‐gated memtransistors allow tunability over the learning rate for non‐Hebbian training where the long‐term potentiation and depression synaptic behavior is dictated by gate biases during the reading and writing processes. Furthermore, the electrostatic control provided by dual gates provides a compact solution to the sneak current problem in traditional memristor crossbar arrays. In this manner, dual gating facilitates the full utilization and integration of memtransistor functionality in highly scaled crossbar circuits. Furthermore, the tunability of long‐term potentiation yields improved linearity and symmetry of weight update rules that are utilized in simulated artificial neural networks to achieve a 94% recognition rate of hand‐written digits.

  2. Abstract

    The device concept of ferroelectric-based negative capacitance (NC) transistors offers a promising route for achieving energy-efficient logic applications that can outperform the conventional semiconductor technology, while viable operation mechanisms remain a central topic of debate. In this work, we report steep slope switching in MoS2transistors back-gated by single-layer polycrystalline PbZr0.35Ti0.65O3. The devices exhibit current switching ratios up to 8 × 106within an ultra-low gate voltage window of$$V_{{{\mathrm{g}}}} = \pm \! 0.5$$Vg=±0.5V and subthreshold swing (SS) as low as 9.7 mV decade−1at room temperature, transcending the 60 mV decade−1Boltzmann limit without involving additional dielectric layers. Theoretical modeling reveals the dominant role of the metastable polar states within domain walls in enabling the NC mode, which is corroborated by the relation between SS and domain wall density. Our findings shed light on a hysteresis-free mechanism for NC operation, providing a simple yet effective material strategy for developing low-power 2D nanoelectronics.

  3. Abstract

    The residue of common photo‐ and electron‐beam resists, such as poly(methyl methacrylate) (PMMA), is often present on the surface of 2D crystals after device fabrication. The residue degrades device properties by decreasing carrier mobility and creating unwanted doping. Here, MoS2and WSe2field effect transistors (FETs) with residue are cleaned by contact mode atomic force microscopy (AFM) and the impact of the residue on: 1) the intrinsic electrical properties, and 2) the effectiveness of electric double layer (EDL) gating are measured. After cleaning, AFM measurements confirm that the surface roughness decreases to its intrinsic state (i.e., ≈0.23 nm for exfoliated MoS2and WSe2) and Raman spectroscopy shows that the characteristic peak intensities (E2gand A1g) increase. PMMA residue causes p‐type doping corresponding to a charge density of ≈7 × 1011cm−2on back‐gated MoS2and WSe2FETs. For FETs gated with polyethylene oxide (PEO)76:CsClO4, removing the residue increases the charge density by 4.5 × 1012cm−2, and the maximum drain current by 247% (statistically significant,p< 0.05). Removing the residue likely allows the ions to be positioned closer to the channel surface, which is essential for achieving the best possible electrostatic gate control in ion‐gated devices.

  4. Abstract

    Ferroelectric (FE) devices are conventionally switched by an application of an electric field. However, the recent discoveries of light–matter interactions in heterostructures based on 2D semiconductors and FE materials open new opportunities for using light as an additional tool for device programming. Recently, a purely optical switching of FE polarization in heterostructures comprising 2D MoS2and FE oxide perovskites, such as BaTiO3and Pb(Zr,Ti)O3(PZT), was demonstrated. In this work, it is investigated whether this optical switching has a practical value and can be used to improve functional characteristics of MoS2‐PZT FE field‐effect transistors for nonvolatile memory applications. It is demonstrated that the combined use of an electrical field and visible light improves the nonvolatile ON/OFF ratios in MoS2‐PZT memories by several orders of magnitude compared to their purely electrical operation. The memories are read at zero gate voltage (VG) in darkness, but their ON and OFF currents, which routinely varied for different devices by over 105, are achieved by programming at the sameVG = −6 V with (ON state) and without (OFF state) light illumination, demonstrating its crucial importance. The light can likely serve as an important tool for better programming of a large variety of other semiconductor‐FE devices.

  5. Abstract

    Metaheuristic algorithms such as simulated annealing (SA) are often implemented for optimization in combinatorial problems, especially for discreet problems. SA employs a stochastic search, where high‐energy transitions (“hill‐climbing”) are allowed with a temperature‐dependent probability to escape local optima. Ising spin glass systems have properties such as spin disorder and “frustration” and provide a discreet combinatorial problem with a high number of metastable states and ground‐state degeneracy. In this work, subthreshold Boltzmann transport is exploited in complementary 2D field‐effect transistors (p‐type WSe2and n‐type MoS2) integrated with an analog, nonvolatile, and programmable floating‐gate memory stack to develop in‐memory computing primitives necessary for energy‐ and area‐efficient hardware acceleration of SA for Ising spin systems. Search acceleration of >800× is demonstrated for 4 × 4 ferromagnetic, antiferromagnetic, and spin glass systems using SA compared to an exhaustive search using a brute force trial at miniscule total energy expenditure of ≈120 nJ. The hardware‐realistic numerical simulations further highlight the astounding benefits of SA in accelerating the search for larger spin lattices.