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Flexible radio frequency (RF) transistors play an important role in the fast-growing wearable smart sensors for data communication. However, the scaling capability and high-speed performance of the flexible transistor are far below the counterparts on rigid substrates, impeding the gigahertz high-speed applications. Here, we address the scaling and performance bottlenecks in flexible transistors by demonstrating natively flexible RF indium tin oxide transistors with deeply scaled 15-nm-long channel, capable of operating in the 10-GHz frequency range. The record-high cutoff frequency of 11.8 GHz and maximum oscillation frequency of 15 GHz can rival those on rigid substrates. Furthermore, the robustness of flexible RF transistors was examined, capable of enduring heavy-duty 10,000 bending cycles at 1-mm radius and extreme thermal stress from cryogenic temperature of 4.3 K and high temperature of 380 K.

In this letter, high-performance zinc oxide thin-film transistors (ZnO TFTs) have been fabricated on Si substrate by atomic layer deposition (ALD) at 190 °C. The field-effect mobility ( $\mu _{FE}$ ) can be improved from 18.5 cm2/ $\text{V}\cdot \text{s}$ to a record high 43.2 cm2/ $\text{V}\cdot \text{s}$ while maintaining a large $\text{I}_{{\mathrm {on}}}/\text{I}_{{\mathrm {off}}}$ ratio of $5\times 10^{9}$ after rapid thermal annealing (RTA) under vacuum at 350 °C. The excellent performance can be attributed to the improvement in the ZnO channel and the interface. The oxygen vacancy ratio in ZnO increases from 36.2% to 40.0%. The interface trap density ( $\text{N}_{it}$ ) between silicon oxide (SiO2) and ZnO decreases from $5.1 \times 10^{11}$ eV $^{-1}$ cm $^{-2}$ to $1.4\times 10^{11}$ eV $^{-1}$ cm $^{-2}$ . Furthermore, the oxide trap density ( $\text{N}_{{\mathrm {ot}}}$ ) of the SiO2 dielectric reduces from $3.7\times 10^{19}$ eV $^{-1}$ cm $^{-3}$ to $1.1\times 10^{19}$ eV $^{-1}$ cm $^{-3}$ . Finally, we systematically study the electrical performance of the annealed ZnO device at measurement temperature from room temperature of 20 °C to a much higher temperature of 180 °C without device failure.

1/f noise provides essential information on the interface trapping effect as well as the scattering mechanism in transistors. In this work, a systematic 1/f noise study has been carried out on the recessed-gate enhancement-mode (E-mode) GaN MOS-HEMTs under electrical and thermal stress together with the depletion-mode (D-mode) counterpart. Low-frequency (1–1000 Hz) measurement has been performed at room (25 °C) and elevated (100 °C) temperatures at different carrier densities at the drain bias of 2 V and 10 V. The results show the E-mode device has much better noise characteristics under high voltage and high temperature compared with the D-mode counterpart. Moreover, charge-noise model reveals that the improved noise behavior of the E-mode device at high density and high drain bias at 100 °C originating from the energy band alignment at high biases, where the D-mode device suffers from extra charge trapping scattering in the gate edge near the gate-to-drain access region.

Low-frequency noise is a key performance-limiting factor in almost all electronic systems. Thanks to its excellent characteristics such as exceptionally high electron mobility, graphene has high potential for future low-noise electronic applications. Here, we present an experimental analysis of low-frequency noise in dual-gate graphene transistors based on chemical vapor-deposited Bernal-stacked bilayer graphene. The fabricated dual-gate bilayer graphene transistors adopt atomic layer-deposited Al2O3 and HfSiO as top-gate and back-gate dielectric, respectively. Our results reveal an obvious M-shape gate-dependent noise behavior which can be well described by a quantitative charge-noise model. The minimal area normalized noise spectral density at 10 Hz reaches as low as about 3 × 10-10 μm2·Hz-1 at room temperature, much lower than the best results reported previously for graphene devices. In addition, the observed noise level further decreases by more than 10 times at temperature of 20 K. Meanwhile, the noise spectral density amplitude can be tuned by more than 2 orders of magnitude at 20 K by dual-gate voltages.

Enhancement-mode (E-mode) GaN MOS-HEMTs using recess process typically face the challenge of precise thickness control, surface roughness issue, and interface traps, all of which could lead to the degradation of the device performance and cause reliability issues. In this article, we use a combined process of atomic layer etching (ALE) technique and atomic layer deposited (ALD) HfSiO dielectric. ALE is repeated oxidation and dry etching process with minimal surface damage, leading to a precisely controlled low-damage recess channel area. The fabricated AlGaN/GaN MOS-HEMTs exhibit E-mode operation with a positive threshold voltage ( ${V}_{\text {th}}$ ) of +2.1 V with small ${V}_{\text {th}}$ dispersion for different devices, an ultrahigh drain current ON– OFF ratio over 1010 and a low ON-resistance ( ${R}_{ \mathrm{\scriptscriptstyle ON}}$ ) of $11.5~\Omega \cdot \text {mm}$ at gate-to-drain length ( ${L}_{\text {GD}}$ ) of $25~\mu \text{m}$ . Source field plate (SFP) structure is employed to reduce the charge trapping process and improve the reliability at high voltages. The current collapse of the E-mode device with SFP structure can be effectively suppressed due to the optimized redistribution of the peak electric field in the gate-to-drain access region, where a significantly improved dynamic ${R}_{ \mathrm{\scriptscriptstyle ON}}$ of only 1.17 times increase from the static ${R}_{ \mathrm{\scriptscriptstyle ON}}$ after OFF-state ${V}_{\text {DS}}$ stress of 600 V. Moreover, the enhanced vertical electric field with decreased AlGaN barrier thickness and the positive shift in threshold voltage for the E-mode device can effectively suppress the current collapse, which outperforms the depletion-mode counterpart. The breakdown voltage reaches a considerable value of 1560 V at an OFF-state current density of ${1}~\mu \text{A}$ /mm.

In this work, a high-performance flexible radio frequency transistor using an ultrathin indium tin oxide film channel based on a solution-cast thin polyimide substrate has been demonstrated. The 60 nm short channel transistor shows a record high cut-off frequency of 5 GHz and a maximum oscillation frequency of 11 GHz with high uniformity among 40 devices. The radio frequency characteristics under various bending conditions have been systematically studied under a bending radius of 5 mm for 10 000 times and a bending radius of 1 mm for 1000 times, showing excellent stability with only 20% decrease in the cut-off frequency. Furthermore, a flexible frequency mixer has also been demonstrated at 2.4 GHz with decent conversion gains.

In this paper, we successfully realized a shortest 10-nm channel length transistor based on ultrathin 3.5-nm indium tin oxide channel. Using 5-nm lanthanum-doped hafnium oxide (HfLaO) high- κ dielectric, the 10- nm channel ultrathin device architecture with wide bandgap exhibits excellent switching behavior with on/off ratio exceeding 1010 and ultra-low leakage current of 40 fA/μm. Record-high on-state current of 1860 μA/μm and transconductance (g m ) of more than 1000 μS/μm have been achieved, benefited from a rather small contact resistance of 162 Ω•μm. R on of the 10-nm ITO transistor was smaller than 500 Ω•μm. Adopting the MIT Virtual Source (MVS) model, we extracted the saturation injection velocity ν x0 up to 8.8 × 106 cm/s and the resulting mean free path λ mfp of ITO transistor is 21.6 nm. Radio frequency transistor with 30-nm-long channel exhibited record high radio-frequency (RF) performance with small-signal current gain (f T ) of 20 GHz and maximum oscillation frequency (f max ) of 13 GHz. These two metrics contribute to $\sqrt {\left( {{f_T} \times {f_{\max }}} \right)} $ exceeding 15 GHz, confirming overwhelming superiority compared to RF transistors based on other ultrathin novel channel materials such as MoS 2 , BP and metal-oxides. Finally, we employed bootstrapped mode (BST) inverters to fabricate a 5-stage ring oscillator, and achieved the record-low propagation delay of 0.4 ns/stage among metal-oxides.

Flexible zinc oxide thin film transistors (ZnO TFTs) with a mobility of $ {13}~\text {cm}^{2}/\text {V}\cdot \text {s}$ and an I $_{\text {on}}/\text{I}_{\text {off}}$ ratio of $ {1.5}\times {10}^{8}$ have been fabricated on polyimide substrate, where the ZnO channel is deposited by atomic layer deposition (ALD) at 140 °C. High bending stability has been achieved due to excellent interface quality between alumina (Al2O3) dielectric and ZnO channel with a sharp interface topography. The flexible ZnO device exhibits excellent electrical characteristics even after being bent for 200 000 cycles with a tensile strain of 0.63%. Electrical measurement under a high tensile strain of 2.08% has also been carried out. Moreover, the electrical performance dependence of flexible ZnO TFTs with a tensile strain of 0.78% on temperature from 20 °C to 140 °C has been investigated for the first time.

Low-frequency noise is a key performance-limiting factor in almost all electronic systems. Thanks to its excellent characteristics such as exceptionally high electron mobility, graphene has high potential for future low-noise electronic applications. Here, we present an experimental analysis of low-frequency noise in dual-gate graphene transistors based on chemical vapor-deposited Bernal-stacked bilayer graphene. The fabricated dual-gate bilayer graphene transistors adopt atomic layer-deposited Al

In this work, ultrathin indium tin oxide (ITO) radio frequency (RF) transistors have been demonstrated for the first time, where inverted gate structure are used with a flexible polyimide substrate using magnetron sputtering at a thermal budget below 200 °C. The 160 nm channel length device exhibits excellent DC characteristics, including mobility of 26 cm2/V•s and an I on /I off ratio of 6.6×108. A record-high extrinsic cut-off frequency (f T ) of 2.1 GHz and an extrinsic maximum oscillation frequency (f max ) of 3.7 GHz have also been obtained, which are more than one order of magnitude higher than previous results on flexible substrate. A high conversion gain of -20.9 dB has been achieved for the gigahertz frequency mixer based on flexible ITO RF transistor. Moreover, the stability of DC and RF performance under different bending conditions up to 50,000 bending cycles or down to 1 mm bending radius are studied without device failure.

In this paper, we report high-speed ultrathin-body (3.5 nm) indium-tin-oxide (ITO) transistors using high-k HfLaO dielectrics with a thickness of 5 nm. Because of its low dielectric constant and large bandgap, ITO is a promising channel material for scaling below the 5 nm regime for advanced low-power electronics with excellent short-channel-immunity. Here, we fabricate sub-100-nm channel length ITO transistors with ultrahigh on/off ratio near 1011 and ultralow off-state current below 10 fA/μm. The 15-nm-long ITO transistor exhibits high performance with the maximum on-state current of 970 μA/μm and peak g m of 400 μS/μm at V ds = 0.5 V. NAND, NOR, and SRAM based on enhancement/depletion mode (E/D) inverters have achieved full rail-to-rail output characteristics and stable memory function. Finally, We demonstrated a stage delay of 0.49 ns/stage for a 5-stage ring oscillator based on bootstrapped mode (BST) inverter, which is the best among all results based on metal-oxides transistors.