Ruixuan Dai

MoS 2 Field-Effect Transistors With Lead Zirconate-Titanate Ferroelectric Gating

We report back gate field-effect transistors (FETs) with few-layered MoS2 nanosheet controlled by lead-zirconate-titanate (PZT) ferroelectric gating. The MoS2 transistors with PZT gating (MoS2-PZT FETs) exhibit reproducible hysteresis and nonvolatile memory behaviors with high stability, which can be attributed to the polarization screening from interface adsorbates and charge dynamic trapping/detrapping into the interface defect states. The ON/OFF states ratios and memory windows have little change with the channel scaling from 2

HfO2 dielectric thickness dependence of electrical properties in graphene field effect transistors with double conductance minima

\mu \text{m}

Adjustable hydrazine modulation of single-wall carbon nanotube network field effect transistors from p-type to n-type

to 200 nm, revealing the channel scaling has not obvious influence on MoS2-PZT FET properties, which suggests MoS2-PZT FET a promising candidate for future non-volatile memory applications.

Controllable Hysteresis and Threshold Voltage of Single-Walled Carbon Nano-tube Transistors with Ferroelectric Polymer Top-Gate Insulators.

We investigate the electrical properties in back-gated graphene field effect transistors (GFETs) with SiO2 dielectric and different thickness of high-k HfO2 dielectric. The results show that transform characteristic (Ids–Vgs) curves of GFETs are uniquely W-shaped with two charge neutrality point (left and right) in both SiO2 and HfO2 dielectric (SiO2-GFETs and HfO2-GFETs). The gate voltage reduces drastically in HfO2-GFETs compared with that in SiO2-GFETs, and it becomes much smaller with the decline of HfO2 thickness. The left charge neutrality point in Id–Vg curves of all HfO2-GFETs is negative, compared to the positive ones in SiO2-GFETs, which means that there exists n-doping in graphene with HfO2 as bottom dielectric. We speculate that this n-doping comes from the HfO2 layer, which brings fixed charged impurities in close proximity to graphene. The carrier mobility is also researched, demonstrating a decreasing trend of hole mobility in HfO2-GFETs contrast to that in SiO2-GFETs. In a series of HfO2-G...

Pentacene organic ferroelectric transistors with [P(VDF-TrFE)] gate by Langmuir-Blodgett process

Single-wall carbon nanotube (SWCNT) network field effect transistors (FETs), which show decent p-type electronic properties, have been fabricated. The use of hydrazine as an aqueous solution and a strong n-type dopant for the SWCNTs is demonstrated in this paper. The electrical properties are obviously tuned by hydrazine treatment at different concentrations on the surface of the SWCNT network FETs. The transport behavior of SWCNTs can be modulated from p-type to n-type, demonstrating the controllable and adjustable doping effect of hydrazine. With a higher concentration of hydrazine, more electrons can be transferred from the hydrazine molecules to the SWCNT network films, thus resulting in a change of threshold voltage, carrier mobility and on-current. By cleaning the device, the hydrazine doping effects vanish, which indicates that the doping effects of hydrazine are reversible. Through x-ray photoelectron spectroscopy (XPS) characterization, the doping effects of hydrazine have also been studied.

Efficient and Reversible Electron Doping of Semiconductor-Enriched Single-Walled Carbon Nanotubes by Using Decamethylcobaltocene

Double-gated field effect transistors have been fabricated using the SWCNT networks as channel layer and the organic ferroelectric P(VDF-TrFE) film spin-coated as top gate insulators. Standard photolithography process has been adopted to achieve the patterning of organic P(VDF-TrFE) films and top-gate electrodes, which is compatible with conventional CMOS process technology. An effective way for modulating the threshold voltage in the channel of P(VDF-TrFE) top-gate transistors under polarization has been reported. The introduction of functional P(VDF-TrFE) gate dielectric also provides us an alternative method to suppress the initial hysteresis of SWCNT networks and obtain a controllable ferroelectric hysteresis behavior. Applied bottom gate voltage has been found to be another effective way to highly control the threshold voltage of the networked SWCNTs based FETs by electrostatic doping effect.

Tunable transfer behaviors of single-layer WSe2 field effect transistors by hydrazine

We report the fabrication and electrical properties of pentacene-based ferroelectric organic field-effect transistors (FeOFETs) with ultrathin poly(vinylidene fluoride trifluoroethylene) [P(VDF-TrFE)] gate insulators. A ultrathin and uniform P(VDF-TrFE) film was successfully deposited by Langmuir-Blodgett (LB) deposition with well-defined ferroelectric microdomains at the interface between P(VDF-TrFE) films and pentacene active layers. The P(VDF-TrFE) films derived by LB deposition significantly enhance the crystallization of the upper pentacene channel films and thus the performance of our FeOFETs. Our FeOFET device achieves a threshold voltage shift of 8.56 V induced by ferroelectric polarization under different voltage sweeping directions and such enhancement indicates a great potential for future organic nonvolatile memory applications.

Temperature-dependent transport and hysteretic behaviors induced by interfacial states in MoS2 field-effect transistors with lead-zirconate-titanate ferroelectric gating

Single-walled carbon nanotubes (SWCNTs) offer great potential for field-effect transistors and integrated circuit applications due to their extraordinary electrical properties. To date, as-made SWCNT transistors are usually p-type in air, and it still remains challenging for realizing n-type devices. Herein, we present efficient and reversible electron doping of semiconductor-enriched single-walled carbon nanotubes (s-SWCNTs) by firstly utilizing decamethylcobaltocene (DMC) deposited by a simple spin-coating process at room temperature as an electron donor. A n-type transistor behavior with high on current, large Ion/Ioff ratio and excellent uniformity is obtained by surface charge transfer from the electron donor DMC to acceptor s-SWCNTs, which is further corroborated by the Raman spectra and the ab initio simulation results. The DMC dopant molecules could be reversibly removed by immersion in N, N-Dimethylformamide solvent, indicating its reversibility and providing another way to control the carrier concentration effectively as well as selective removal of surface dopants on demand. Furthermore, the n-type behaviors including threshold voltage, on current, field-effect mobility, contact resistances, etc. are well controllable by adjusting the surface doping concentration. This work paves the way to explore and obtain high-performance n-type nanotubes for future complementary CMOS circuit and system applications.

High-performance heterogeneous complementary inverters based on n-channel MoS2 and p-channel SWCNT transistors

Polarity modulation of single-layer WSe2 field effect transistor is investigated by using hydrazine as a solution-processable and effective n-type dopant for WSe2. Compared to the intrinsic hole-dominant ambipolar behaviors, highly effective n-type doping characteristics are achieved after hydrazine treatment. It is found that the on-current improves obviously by one order of magnitude and the metal-WSe2 contact resistance decreases at the same time. After hydrazine being removed, the electron doping effect disappears which indicates hydrazine treatment is a reversible doping process. This work provides a possibility for transition metal dichalcogenides-based logic device applications in the future.

Tunable hysteresis behaviors in perovskite transistors

We report back gate field-effect transistors (FETs) with few-layered MoS2 nanosheet controlled by lead-zirconate-titanate (PZT) ferroelectric gating. The MoS2 transistors with PZT gating (MoS2-PZT FETs) exhibit reproducible hysteresis and nonvolatile memory behaviors with high stability, which can be attributed to the polarization screening from interface adsorbates and charge dynamic trapping/detrapping into the interface defect states. The ON/OFF states ratios and memory windows have little change with the channel scaling from 2 μm to 200 nm, revealing the channel scaling has not obvious influence on MoS2-PZT FET properties, which suggests MoS2-PZT FET a promising candidate for future non-volatile memory applications.