Showing papers by "Xiaohua Ma published in 2023"

Printable Epsilon‐Type Structure Transistor Arrays with Highly Reliable Physical Unclonable Functions

Abstract: Printed electronics promises to drive the future data‐intensive technologies, with its potential to fabricate novel devices over a large area with low cost on nontraditional substrates. In these emerging technologies, there exists a large digital information flow, which requires secure communication and authentication. Physical unclonable functions (PUFs) offer a promising built‐in hardware‐security system comparable to biometrical data, which can be constructed by device‐specific intrinsic variations in the additive manufacturing process of active devices. However, printed PUFs typically exploit the inherent variation in layer thickness and roughness of active devices. The current in devices with enough significant changes to increase the robustness to external environment noise is still a challenge. Here, printable epsilon‐type‐structure indium tin oxide transistor arrays are demonstrated to construct high‐reliability PUFs by modifying the coffee‐ring structure. The epsilon‐type structure improves the printing scalability, film quality, and device reliability. Furthermore, the print‐induced uncertainty along the channel thickness and length can lead to changes in the carrier concentration. Notably, the randomly distributed printing droplets in a small area significantly increase this uncertainty. As a result, the PUFs exhibit near‐ideal uniformity, uniqueness, randomness, and reliability. Additionally, the PUFs are resilient against machine‐learning‐based attacks with a prediction accuracy of only 55% without postprocessing.

Design of a 17–24-GHz High-Efficiency Power Amplifier for Satellite Communications

Abstract: In this letter, a ${K}$ -band high-efficiency power amplifier (PA) design using modified resistive-reactive hybrid continuous modes (HCMs) is presented. These modified modes can increase the real part of the fundamental impedance when the second harmonic impedances become resistive-reactive. This helps to reduce the impedance transformation ratio when applying modified modes in transistors with a small optimal impedance ( ${R} _{\rm opt}$ ), as well as making HCMs more practical in these transistors. For ${K}$ -band Satcom downlink applications, by using this method, combined with a compact output matching network (OMN) design, high performance, and high integration PA can be achieved. A $2\times1.2$ mm GaAs pHEMT PA operating at 17–24 GHz was designed and fabricated to verify the theory. Continuous wave measurements show that the saturation output power is greater than 0.5 W and an average power-added efficiency (PAE) of 42%.

Improved switching stability in SiNx-based RRAM by introducing nitride insertion layer with high conductivity

Abstract: In this Letter, a Pt/SiNx/TiN/Ta resistive random access memory (RRAM) is proposed, which has low switching voltage, uniform resistance distribution, excellent cycle-to-cycle stability, and excellent nonvolatile performance. As an insertion layer, TiN prevents excessive absorption of nitrogen ions by a Ta electrode and avoids the formation of the unstable metal–semiconductor interface, which significantly reduces cycle-to-cycle variability of SiNx-based RRAM. Due to high conductivity, the TiN layer has a small voltage divider effect when voltage was applied, which helps to achieve low power consumption characteristics. This paper provides a direction for improving performance of nitride-based RRAM, which is useful for further development of highly reliable RRAM.

All‐in‐One Compression and Encryption Engine Based on Flexible Polyimide Memristor

Abstract: It is anticipated that the rapid development of the Internet of Things (IoT) will improve the quality of human life. Nonetheless, large amounts of data need to be replicated, stored, processed, and shared, posing formidable challenges to communication bandwidth and information security. Herein, it is reported that polyimide (PI) threshold‐switching memristors exhibit Gaussian conductance and randomly set voltage distribution with nonideal properties to create a compression and encryption engine with a single chip. The Gaussian conductance distribution is used to achieve compressed sensing (CS) to integrate encryption into compression, and the spontaneous formation of the one‐time‐sampling measurement matrix satisfies absolute security. Moreover, the bitstreams generated by randomly distributed set voltages are used to diffuse the ciphertext from CS to improve security. The engine is shown to be secure even if the eavesdropper knows both the plaintext and the corresponding ciphertext. It has compression performance advantages that take both efficiency and security into account. In addition, due to the superior high temperature and mechanical properties of PI, the engine can continue to function normally in harsh environments. Herein, an excellent solution is offered for ensuring the efficiency and security of IoT.

Biodegradable and flexible artificial nociceptor based on Mg/MgO threshold switching memristor

Abstract: As an important receptor located in the skin, a nociceptor is capable of detecting noxious stimuli and sending warning signals to the central nervous system to avoid tissue damage, thus inspiring the development of artificial nociceptors for electronic receptors. Recently, memristors have attracted increasing attention for developing artificial nociceptors due to the simplicity of the artificial nociceptive system. However, the realization of artificial nociceptors with biocompatibility and biodegradability in a single memristive device remains a challenge. Herein, a fully biocompatible and biodegradable threshold switching (TS) memristor consisting of W/MgO/Mg/W configuration was proposed as an artificial nociceptor. The device showed unidirectional TS characteristics with stable electrical performance under bending conditions. Critical nociceptor behaviors, including threshold, relaxation, no adaptation, allodynia, and hyperalgesia, were successfully demonstrated in the memristive nociceptor. Meanwhile, an optoelectronic nociceptor system was built by the integration of a photoresistor and the memristor. Importantly, the devices transferred on a biodegradable polyvinyl acetate substrate as physically transient electronics could completely dissolve in deionized water, simulating the decomposition of skin necrosis. This study provides a novel route toward developing fully biocompatible and biodegradable artificial nociceptors for promising applications in implantable and wearable electronics and secure bio-integrated systems.

Multi-functional MXene quantum dots enhance the quality of perovskite polycrystalline films and charge transport for solar cells.

Abstract: Recently, two-dimensional (2D) transition metal carbides/nitrides (MXenes) find applications in perovskite solar cells (PSCs), due to their high conductivity, tunable electronic structures, and rich surface chemistry, etc. However, the integration of 2D MXenes into PSCs is limited by their large lateral sizes and relatively-small surface volume ratios, and the roles of MXenes in PSCs are still ambiguous. In this paper, zero-dimensional (0D) MXene quantum dots (MQDs) with an average size of 2.7 nm are obtained through clipping step by step combining a chemical etching and a hydrothermal reaction, which display rich terminals (i.e., -F, -OH, -O) and unique optical properties. The 0D MQDs incorporated into SnO2 electron transport layers (ETLs) of PSCs exhibit multifunction: 1) increasing the electrical conductivity of SnO2, 2) promoting better alignments of energy band positions at the perovskite/ETL interface, 3) improving the film quality of atop polycrystalline perovskite. Particularly, the MQDs not only tightly bond with the Sn atom for decreasing the defects of SnO2, but also interact with the Pb2+ of perovskite. As a result, the defect density of PSCs is significantly decreased from 5.21 × 1021 to 6.4 × 1020 cm-3, leading to enhanced charge transport and reduced nonradiative recombination. Furthermore, the power conversion efficiency (PCE) of PSCs is substantially improved from 17.44% to 21.63% using the MQDs-SnO2 hybrid ETL compared with the SnO2 ETL. Besides, the stability of the MQDs-SnO2-based PSC is greatly enhanced, with only ～4% degradation of the initial PCE after storage in ambient condition (25 °C, RH: 30-40%) for 1128 h, as compared to that of the reference device with a rapid degradation of ～60% of initial PCE after 460 h. And MQDs-SnO2-based PSC also presents higher thermal stability than SnO2-based device with continuous heating for 248 h at 85 °C. The unique MQDs exhibited in this work might also find other exciting applications such as light-emitting diodes, photodetectors, and fluorescent probes.

Solvent-free fabrication of broadband WS2 photodetectors on paper

Abstract: Paper-based devices have attracted extensive attention due to the growing demand for disposable flexible electronics. Herein, we integrate semiconducting devices on cellulose paper substrate through a simple abrasion technique that yields high-performance photodetectors. A solvent-free WS₂ film deposited on paper favors an effective electron-hole separation and hampers recombination. The as-prepared paper-based WS₂ photodetectors exhibit a sensitive photoresponse over a wide spectral range spanning from ultraviolet (365 nm) to near-infrared (940 nm). Their responsivity value reaches up to ~270 mA W⁻¹ at 35 V under a power density of 35 mW cm⁻². A high performance photodetector was achieved by controlling the environmental exposure as the ambient oxygen molecules were found to decrease the photoresponse and stability of the WS₂ photodetector. Furthermore, we have built a spectrometer using such a paper-based WS₂ device as the photodetecting component to illustrate its potential application. The present work could promote the development of cost-effective disposable photodetection devices.

Transient form of polyvinyl alcohol-based devices with configurable resistive switching behavior for security neuromorphic computing

Abstract: Physically transient resistive switching devices, a form of memory devices with the ability of achieving physical disappearance in a controllable manner, hold tremendous potentials in multiple security applications. Herein, we demonstrated a physically transient form of memristive device composed of Ag/polyvinyl alcohol/W with configurable resistive switching functionality for security neuromorphic computing. The resistive switching type of the transient device could be modulated effectively by controlling the compliance current during the set process, which was well interpreted by the filament model. Typical synaptic functions pertained to short-term plasticity (STP) and its transition from STP to long-term plasticity were vividly mimicked in this transient memristive device. Importantly, both the synaptic functions and physical form of the transient devices were capable of disappearing instantly upon immersing in de-ionized water, and the dissolution characteristics of the constituent transient materials were investigated experimentally to reveal the degradation mechanism of the device. This transient form of artificial synapse provides foreseeing perspectives on information security enhancement for neuromorphic computing systems.

High-Efficiency Millimeter-Wave Enhancement-Mode Ultrathin-Barrier AlGaN/GaN Fin-HEMT for Low-Voltage Terminal Applications

Abstract: In this work, high-efficiency millimeter-wave enhancement-mode (E-mode) Fin-high electron mobility transistor (HEMT) is fabricated to satisfy low-voltage terminal applications, whose fabrication process is performed on the in situ SiN passivated ultrathin-barrier AlGaN/GaN heterojunction and features N $_{\text{2}}$ O plasma oxidation treatment on the fins. Specifically, the fabricated E-mode Fin-HEMT exhibits a positive threshold voltage of 0.3 V, at the cost of decreased maximum output current density of 483 mA/mm and lowered peak extrinsic transconductance of 277 mS/mm. Comfortingly, a reduced knee voltage of 1.5 V together with suppressed OFF-state leakage current of 6 $\times$ 10 $^{-\text{6}}$ mA/mm is also obtained for Fin-HEMT. Besides, an OFF-state breakdown voltage of 38 V is achieved, which is sufficiently high to meet the low-voltage RF device’s need for breakdown voltage. Pulsed $\textit{I}$ – $\textit{V}$ measurement shows that a negligible current collapse (CC) is achieved for Fin-HEMT. Additionally, Fin-HEMT demonstrates a good stability by stress reliability test. Subsequently, the $\textit{f}_{\textit{T}}$ / $\textit{f}_{\text{MAX}}$ value of 40/86 GHz is obtained for Fin-HEMT at $\textit{V}_{\text{DS}}$ of 6 V by small signal measurement. Eventually, the millimeter-wave low-voltage load pull measurement shows that the fabricated E-mode Fin-HEMT is able to deliver a decent power added efficiency (PAE) of 55% at 30 GHz and $\textit{V}_{\text{DS}}$ of 6 V, revealing the great potential of the fin configuration combined with ultrathin-barrier AlGaN/GaN heterojunction passivated by in situ SiN and N $_{\text{2}}$ O plasma oxidation treatment in high-efficiency millimeter-wave low-voltage terminal applications.

Investigation of multi-fingers drain field plate in dual-threshold coupling AlGaN/GaN HEMTs for optimizing linearity at high electrical field in Ka-bands

Abstract: GaN-High-electron-mobility transistors (GaN-HEMTs) were fabricated and investigated in detail to improve the linearity at high operation voltage. The scheme of dual-threshold coupling was adopted to mitigate the transconductance (Gm) non-linearity, and multi-finger drain field plate was employed to alleviate the high electric field. The proposed devices yielded Gm plateau of 5.5 V, 10 dB improvement in output third order intercept power. The load-pull measurements at 30 GHz delivered peak power-added-efficiency of 52.5 %, and saturation output-power-density of 5.5 W/mm, whose 2.4 dB improvement in gain compression, and 2 dB enhancement in 1-dB compression point, respectively.

Bio‐Voltage Memristors: From Physical Mechanisms to Neuromorphic Interfaces

Abstract: With the rapid development of emerging artificial intelligence technology, brain–computer interfaces are gradually moving from science fiction to reality, which has broad application prospects in the field of intelligent robots. Looking for devices that can connect and communicate with living biological tissues is expected to realize brain–computer interfaces and biological integration interfaces. Brain‐like neuromorphic devices based on memristors may have profound implications for bridging electronic neuromorphic and biological nervous systems. Ultra‐low working voltage is required if memristors are to be connected directly to biological nerve signals. Therefore, inspired by the high‐efficient computing and low power consumption of biological brain, memristors directly driven by the electrical signaling requirements of biological systems (bio‐voltage) are not only meaningful for low power neuromorphic computing but also very suitable to facilitate the integrated interactions with living biological cells. Herein, attention is focused on a detailed analysis of a rich variety of physical mechanisms underlying the various switching behaviors of bio‐voltage memristors. Next, the development of bio‐voltage memristors, from simulating artificial synaptic and neuronal functions to broad application prospects based on neuromorphic computing and bio‐electronic interfaces, is further reviewed. Furthermore, the challenges and the outlook of bio‐voltage memristors over the research field are discussed.

Terahertz monolithic integrated narrow-band filter based on the silicon carbide substrate

Abstract: This paper presented a narrow-band terahertz integrated cavity filter based on the silicon carbide (SiC) substrate. By introducing two metalized via-holes in a rectangular integrated cavity, an integrated coupling cavity was built, on the one hand, to operate as a coupling structure; on the other hand, to control the direct coupling between input and output feeding lines, further to control the frequency of the transmission zero. This novel approach was thoroughly investigated with attention paid to the position of the via-holes. Based on this approach, a terahertz narrow-band filter was realized on the semi-insulating SiC substrate, demonstrated good filtering performance, especially the stopband rejection characteristic, and established the groundwork for the production of the terahertz monolithic integrated circuit.

Investigation on GaN-Based Double-Channel p-Heterostructure Field-Effect Transistors with a p-GaN Insertion Layer

Abstract: GaN-based p-channel heterostructure field-effect transistors (p-HFETs) face significant constraints on the on-state currents compared to the n-channel high electron mobility transistors (n-HEMTs). In this work, we propose a novel double-heterostructure which introduces an additional p-GaN insertion layer into the traditional p-HFETs. The impact of the device structure on the hole densities and valence band energies of both the upper and lower channels is analyzed by using Silvaco TACD simulations, including the thickness of the upper AlGaN layer and the doping impurities and concentration in the GaN buffer layer, as well as the thickness and Mg doping concentration in the p-GaN insertion layer. With the help of the p-GaN insertion layer, the C-doping concentration in the GaN buffer layer can be reduced, while the density of two-dimensional hole gas (2DHG) in the lower channel is enhanced at the same time. This work suggests that the double heterostructure with a p-GaN insertion layer is a better approach to improve p-HFETs compared to those devices with C-doped buffer layer alone.

Physical Mechanism of the β‐Ga2O3 PN Tunneling Diode with a Low Specific On‐Resistance

Abstract: This study proposes a β‐Ga2O3 pn tunneling diode (PNT‐diode) in which the p‐type region is obtained by sputtering a thin NiOx layer in the pure argon atmosphere. The diode exhibits good characteristics: a high current density of 1530 A cm−2 at 10 V and a low specific on‐resistance of 0.56 mΩ cm2. Moreover, its breakdown voltage of is about four times compared to a conventional diode, and its Baliga's figure of merit (BFOM) is as high as 3.25 GW cm−2. Ni/NiOx diodes are simulated by Silvaco simulation software to investigate the physical mechanism of the low specific on‐resistance of the PNT‐diode, and the results demonstrate that Ni and NiOx can form a reverse diode, and that PNT‐diode is equivalent to the Ni/NiOx reverse diode and the NiOx/β‐Ga2O3 forward diode connected in series. Finally, the electric field distribution of the PNT‐diode is simulated, and it is found that p‐type NiOx can significantly reduce the peak electric field at the anode edge.

Research on the β-Ga2O3 Schottky barrier diodes with oxygen-containing plasma treatment

Abstract: This Letter reports two kinds of oxygen-containing plasma treated β-Ga2O3 Schottky barrier diodes (SBDs), including N2O plasma treatment and O2 plasma treatment, and the SBD without plasma is prepared for comparison. I–V characteristics, breakdown characteristics, and trap state characteristics of three devices have been studied. It is found that the turn-on voltage of SBDs with N2O plasma can reduce to 0.6 V, and the better current density of 750 A/cm2 and an on-resistance of 3.5 mΩ cm2 are obtained after the N2O plasma treatment. Moreover, the breakdown voltage of SBDs with N2O plasma is 50.2% higher than the conventional one, whose value reaches 323 V. In addition, the trap states' characteristics of the devices are studied, which show that the oxygen-containing plasma can reduce the deep level trap states density partly in the anode region, which can improve the surface quality effectively.

High Linear and Temperature Insensitive GaAs Power Amplifier Operating at 3.3–3.6 GHz Using a Multi-Feedback Branch Bias Circuit

Abstract: This letter describes a design of a 3.3–3.6-GHz GaAs heterojunction bipolar transistor (HBT) power amplifier (PA) with high linearity and temperature insensitivity for the fifth-generation (5G) of new radios (NRs). By involving a multi-feedback branches bias circuit, the voltage at the feedback node of the bias circuit can achieve dynamic self-tuning to stabilize the base voltage as the amplifier’s input power grows and stabilize the bias current as the temperature increases as well. A three-stage common source structure PA in the form of a monolithic microwave integrated circuit (MMIC) is designed using a multi-feedback branch bias circuit with a size of $1.5\times1.2$ mm. Measured with continuous wave (CW) signals, the output 1-dB compression point at 3.3–3.6 GHz is 34 dBm. The linearity of the PA is also evaluated using a 5G-NR 100-MHz 64-quadratic-amplitude modulated (QAM)-orthogonal frequency division multiplexing (OFDM) signal with a 7-dB peak-to-average-power ratio (PAPR). The proposed PA achieves an adjacent channel power ratio (ACPR) less than −49.5 dBc at an average power of 28 dBm with a power-added efficiency (PAE) of 20% without the use of digital pre-distortion (DPD). In the temperature range of $- 40\,\,^{\circ }\text{C}$ to 120 °C, the variance of bias current, small signal gain, PAE, output power at 1-dB compression point (OP1dB), and ACPR is relatively minor. This design is ideally suited for 5G communication systems due to its high linearity and temperature insensitivity.

An Electro-Thermal Co-Designed Ga2O3[100] Trench Power Diode Featuring Ferroelectric Dielectric

Abstract: One major roadblock toward the maturation of Ga2O3 technology is device overheating. For Ga2O3 trench devices, although with the higher thermal conductivity (kT[010]) of [100] trench sidewall compared to [010] trench sidewall, the Ga2O3 trench devices with [100] trench are rarely adopted, due to the worst sidewall interface quality induced by sidewall-orientation-dependent etch damage, even after the wet etch repair using acids. For the first time, the proposed electro-thermal co-designed Ga2O3 [100] trench diode based on optimized trench sidewall interface quality, featuring ferroelectric dielectric, exhibits better performance compared with Ga2O3 [010] trench diode. Under the identical power consumption, the Ga2O3 [100] trench diode shows the lowest center junction temperature, which is 9 degree lower than that of Ga2O3 [010] trench diode. The new interface-quality optimization strategy can significantly provide potential for electro-thermal optimization of Ga2O3 trench devices.

Effects of Neutron Irradiation on Electrical Performance of β-Ga2 O3 Schottky Barrier Diodes

Abstract: The effect of neutron irradiation on the electrical performance of the $\beta $ -Ga2O3 Schottky barrier diode (SBD) device has been studied in this work. After equivalent 1 MeV neutron irradiation with a fluence of $1\times 10^{{14}}$ n/cm2, a 20% decrease in the forward current density ( ${J}_{\text {F}}{)}$ , a 75% reduction in the reverse current density ( ${J}_{\text {R}}{)}$ , and a 300 V increase in the breakdown voltage ( ${V}_{\text {br}}{)}$ have been observed according to current–voltage ( ${I}$ – ${V}{)}$ measurements. Utilizing the frequency-dependent conductance technique, it is found that the density of interface states located at Pt/Ga2O3 increases slightly from $2.6\times 10^{{12}}$ – $6.4\times 10^{{12}}$ to $2.9\times 10^{{12}}$ – $7.0\times 10^{{12}}$ cm $^{-{2}}$ eV $^{-{1}}$ with an increase in trap activation energy from 0.09–0.122 to 0.096–0.134 eV after neutron irradiation. Furthermore, based on the capacitance–voltage ( ${C}$ – ${V}{)}$ measurement, it is observed that the carrier concentration across the Ga2O3 drift layer was decreased from $1.80\times 10^{{16}}$ to $1.35\times 10^{{16}}$ cm $^{-{3}}$ after neutron irradiation. Considering the device performance change, it indicates that the bulk traps within the Ga2O3 drift layer instead of interface states dominate the device degradation.

High Current and Linearity AlGaN/GaN/-Graded-AlGaN:Si-doped/GaN Heterostructure for Low Voltage Power Amplifier Application

Abstract: In this letter, the AlGaN/GaN/graded-AlGaN:Si-doped/GaN double channel (GDC-SI) high electronic mobility transistors (HEMTs) with high saturation current density and linearity have been reported for low voltage applications. Compared with the standard AlGaN/GaN/AlGaN/GaN double channel GaN (SDC) HEMTs, the GDC-SI HEMTs exhibited the higher saturation current, the broader and flatter transconductance profile, the lower transconductance ( ${g}_{\text {m}}{)}$ derivatives, and lower on-resistance ( ${R}_{\text {on}}{)}$ . Due to the Si-doped graded bottom barrier present in GDC-SI HEMTs, the profile of current gain cutoff frequency ( ${f}_{\text {T}}{)}$ and the maximum oscillation frequency ( ${f}_{\text {max}}{)}$ were flatter with the bias voltage increased. The output power density of 0.75 W/mm and power added efficiency (PAE) of 58% were achieved for GDC-SI HEMTs, at the drain voltage of 7 V and the test frequency of 3.6GHz. The output third-order intercept point (OIP3) of 39.3 dBm and saturation current density of 1909 mA/mm are achieved, which are the state-of-the-art saturation current and OIP3 in the double-channel GaN HEMTs.

Characterization of different trap states in AlGaN/GaN MIS-HEMTs under high reverse gate stress

Abstract: In this work, we have studied the degradation of AlGaN/GaN MIS-HEMTs under reverse gate stress. It found that the origin of the threshold voltage shift (ΔVTH) is not derived from the barrier layer defect, but is closely related to the gate dielectric layer. In order to investigate it, two types of trap states (traps A and B) with different properties in AlGaN/GaN MIS-HEMTs gate dielectrics were proposed and studied by the constant stress-recovery experiment and thermal detrapping technique. Trap A is related to the precursor defect with transient characteristics. Trap B with permanent characteristics is newly generated during the stress, which dominates the permanent degradation and induces the breakdown. Furthermore, according to the measurement results of ΔVTH and injected-electron density (Ninj), the capture cross sections of traps A and B have been extracted, which are 5.52 × 10−21cm2 and 1.38 × 10−22cm2, respectively.