Gate Electrode Research Articles

Work Function Estimation of Gallium-Doped Zinc Oxide Using Transparent Gate Electrode MOSFET

In this research, the work function (WF) of RF sputtered GZO thin films has been estimated using the electrical characteristics n-Metal Oxide Semiconductor Field Effect Transistor (n-MOSFET) device. Two identical sets of MOSFETs were fabricated in this work using a four-level mask. These MOSFETs have two different types of gate contact materials (Al and GZO respectively). GZO was deposited by using RF magnetron sputtering technique while Al was deposited using the thermal evaporation technique. By comparison of the work function of the two MOSFETs, the work function of RF sputtered GZO thin films was identified to be around 4.58 eV.

Electron-beam lithography of nanostructures at the tips of scanning probe cantilevers

We developed a process to fabricate nanoscale metallic gate electrodes on scanning probe cantilevers, including on the irregular surface of protruding cantilever tips. The process includes a floating-layer technique to coat the cantilevers in an electron-beam resist. We demonstrate gate definition through a lift-off process and through an etching process. The cantilevers maintain a high force sensitivity after undergoing the patterning process. Our method allows the patterning of nanoscale devices on fragile scanning probes, extending their functionality as sensors.

Mobility Enhancement Induced by Oxygen Gettering of TiAl for Metal Gated NMOSFETs

In this work, the influence of TiAl gate electrodes fabricated by physical vapor deposition (PVD) and atomic layer deposition (ALD) on electron mobility for metal-gated NMOSFETs is respectively investigated. Due to the specific production chemistry, the ALD TiAl film inherently contains lots of C atoms, which further suppresses its O-gettering capability. Compared to the ALD TiAl device, about 15% higher peak mobility for the PVD TiAl device is demonstrated, which is attributed to the lower bulk trap density in gate dielectric layers as revealed by the 1/ <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">${f}$ </tex-math></inline-formula> noise characteristics analysis. By means of the energy dispersive X-ray spectroscopy (EDX) and X-ray photoelectron spectroscopy (XPS) analysis, the reduced trap density is related to the fact that PVD TiAl can extract more O atoms from gate dielectric layers than ALD TiAl, which weakens the electron trapping/de-trapping process and correspondingly enhances the mobility.

Investigation on the threshold voltage instability mechanism of p-GaN gate AlGaN/GaN HEMTs under high-temperature reverse bias stress

In this Letter, threshold voltage instability of p-GaN gate AlGaN/GaN HEMTs under high-temperature reverse bias (HTRB) stress has been investigated in detail. The experimental results show that the threshold voltage increases by 0.62 V after 100 ks stress at 200 °C. Especially, the degradation phenomenon is unrecoverable. A deep-level transient spectroscopy (DLTS) technique is used to characterize the defect evolution process during the stress. Two kinds of electron traps within the p-GaN layer were proposed to explain the degradation, which were generated by the injected high-energy electrons from the gate electrode. One is referred to as fixed charge trap, and another is trap E3 (EC-0.7 eV). With the aid of high temperature, more electrons are injected and trapped in the fixed charge trap, which causes the permanent threshold voltage increase. In addition, the concentration and capture cross section of trap E3 were extracted as well, which are considered to dominate the recoverable degradation of the device due to the relatively shallower energy level.

A novel high-low-high Schottky barrier based bidirectional tunnel field effect transistor

In this work, we proposed a novel High-Low-High Schottky barrier bidirectional tunnel field effect transistor (HLHSB-BTFET). Compared with previous technology which is named as High Schottky barrier BTFET (HSB-BTFET), the proposed HLHSB-BTFET requires only one gate electrode with independent power supply. More importantly, take an N type HLHSB-BTFET as an example, different from the previously proposed HSB-BTFET, due to that the effective potential of the central metal is increased with the increasing of drain to source voltage (Vds), built-in barrier heights maintain at the same value when the Vds is increased. Therefore, there is no strong dependence between built-in barrier heights formed in the semiconductor region on the drain side and the Vds. Besides that low Schottky barrier formed on the interface between the conduction band of silicon regions on its both sides and the central metal (while high Schottky barrier formed between the valence band of silicon regions on its both sides and the central metal) have been designed for preventing the carriers in valence band from flowing into the central metal induced by thermionic emission effect. Thereafter, the proposed N type HLHSB-BTFET has a natural blocking effect on the carriers flowing in valence band, and this blocking effect is not significantly degraded with the increasing of Vds, which is a huge promotion from the previous technology. The comparison between the two technologies is carried out, which exactly agrees with the design assumptions.

Effects of gate roughness on low voltage InGaZnO thin-film transistors with ultra-thin anodized AlxOy dielectrics

Low-voltage oxide semiconductors thin-film transistors (TFTs) with ultra-thin dielectrics are gaining attention in wearable electronics. However, it is a challenge for oxide semiconductor TFTs to operate at a low-voltage while maintaining high performance. In this article, ultra-thin Al x O y films (∼3 nm) are grown on aluminum (Al) electrodes with different surface roughness by anodization. The morphology and electrical properties of the anodized Al x O y films are studied. Furthermore, InGaZnO (IGZO) TFTs with the anodized AlxOy dielectrics are fabricated. It is revealed that the rougher Al gate electrode deposition resulted in a higher interface trap density, which lead to the degradation of device performance. Through optimizing the surface roughness of the initial Al gate electrodes that are used for anodization, the IGZO TFTs can operate at 1 V and show desirable properties including a reasonable saturation mobility of 5.5 cm2 V−1s−1, a low threshold voltage of 0.37 V, a small subthreshold swing of 79 mV decade−1, and a high current on-off ratio of over 106. This work shows the potential of using anodization in the future for low-power wearable electronics.

Enhancing the repeatability and sensitivity of low-cost PCB, pH-sensitive field-effect transistors

Discrete, extended gate pH-sensitive field-effect transistors (dEGFETs) fabricated on printed circuit boards (PCBs) are a low-cost, simple to manufacture analytical technology that can be applied to a wide range of applications. Electrodeposited iridium oxide (IrOx) films have emerged as promising pH-sensitive layers owing to their theoretically high pH sensitivity and facile deposition, but typically exhibit low pH sensitivity or lack reproducibility. Moreover, to date, a combined IrOx and dEGFET PCB system has not yet been realised. In this study, we demonstrate a dEGFET pH sensor based on an extended gate manufactured on PCB that is rendered pH sensitive through an electrodeposited IrOx film, which can reliably and repeatably display beyond-Nernstian pH response. Using a combination of complementary surface analysis techniques, we show that the high pH sensitivity and repeatability of the dEGFETs are dependent on both the chemical composition and critically the uniformity of the IrOx film. The IrOx film uniformity can be enhanced through electrochemical polishing of the extended gate electrode prior to electrodeposition, leading to dEGFETs that exhibit a median pH sensitivity of 70.7 ± 5 mV/pH (n = 56) compared to only 31.3 ± 14 mV/pH (n = 31) for IrOx electrodeposited on non-polished PCB electrodes. Finally, we demonstrate the applicability of these devices by demonstrating the detection and quantification of ampicillin due to β-Lactamase enzyme activity, thus laying the foundation for cheap and ubiquitous sensors which can be applied to a range of global challenges across healthcare and environmental monitoring.

Textile-based dual-mode organic electrochemical transistors for lactate biosensing

The dual-mode organic electrochemical transistors (OECT) were successfully assembled on fabric. The property of different devices has been compared. In the depletion mode, the PEDOT: PSS/textile-based OECT exhibit high transconductance of 75 mS, and the switching ratio of 8 × 102. In accumulation mode, the PEDOT: PSS/DETA/textile-based OECT exhibit transconductance of 0.55 mS, switching ratio can reach 31.7. Both modes have good cycle stability. A lactate (LA) sensor was prepared by modifying the gate electrode with lactate oxidase. The sensitivity of the sensor is 69.97 mV/decade and 47.8 mV/decade in the depletion and accumulation mode, respectively. The LA sensor in both modes has good linear response in a wide concentration range of 100 pM-10 mM. The sensor has been successfully applied to the detection of LA in sweat sample. It has the advantages of simple preparation, good performance, and convenient integration into clothes, which provides a feasible platform for intelligent wearable and portable medical detection.

Fully-Solution-Processed Enhancement-Mode Complementary Metal-Oxide-Semiconductor Carbon Nanotube Thin Film Transistors Based on BiI3 -Doped Crosslinked Poly(4-Vinylphenol) Dielectrics for Ultralow-Power Flexible Electronics.

The threshold voltage (Vth ) adjustment of complementary metal-oxide-semiconductor (CMOS) thin film transistors (TFTs) is one of the research hotspotsdue to its key role in energy consumption control of CMOS circuits. Here, ultralow-power flexible CMOS circuits based on well-matched enhancement-mode (E-mode) CMOS single-walled carbon nanotube (SWCNT) TFTs are successfully achieved through tuning the work function of gate electrodes, electron doping, and printing techniques. E-mode P-type CMOS SWCNT TFTs with the full-solution procedure are first obtained through decreasing the work function ofAg gate electrodes directly caused by the deposition of bismuth iodide(BiI3 )-doped solid-state electrolyte dielectrics. After synthetic optimization of dielectric compositions and semiconductor printing process, the flexible printed E-mode SWCNT TFTs show the high Ion /Ioff ratios of ≈106 , small subthreshold swing (SS) of 70-85mV dec-1 ,lowoperating voltages of ≈0.5 to -1.5V, good stabilityand excellent mechanical flexibility during 10000 bending cycles. E-mode N-type SWCNT TFTs are then selectively achieved via printing the polarity conversion ink (2-Amino-2-methyl-1-propanol (AMP) aselectron dopingagent) in P- type TFT channels. Last, printed SWCNT CMOS invertersare successfully constructed with full rail-to-rail output characteristics and the record unit static power consumption of 6.75 fW µm-1 at VDD of 0.2V.

All-Carbon Solution-Gated Transistor with Low Operating Voltages for Highly Selective and Stable Dopamine Sensing.

The diversity of carbon materials makes it possible to prepare all-carbon electronic devices requiring components with different properties and functions. In this work, we fabricate an all-carbon solution-gated transistor (AC-SGT) based dopamine (DA) sensor with Nafion coated nitrogen and oxygen co-doped carbon yarn (Nafion/NOCY) as the gate electrode and graphene as the channel. The carbon materials in AC-SGT render the usage of a variety of strategies to improve its electrochemical sensing capability including the modification of the gate electrode and the modulation of the operating voltage. With a low gate-source voltage of 0.02 V as well as a low drain-source voltage of 0.05 V, AC-SGT manifests the outstanding DA sensing performances in terms of sensitivity, selectivity, limit of detection (3 nM, S/N > 3), linear range (3 nM to 300 μM), long-term stability (over 30 days), and preconditioning time (60 s). Furthermore, a smartphone controlled portable sensing system integrated with AC-SGT is fabricated herein, which shows the excellent in vitro sensing capability of DA in urine, proving the potential of all-carbon transistors in smart wearable biosensors.

Fabrication of a Novel and Ultrasensitive Label-Free Electrochemical Aptasensor Based on Gold Nanostructure for Detection of Homocysteine

The current attempt was made to detect the amino acid homocysteine (HMC) using an electrochemical aptasensor. A high-specificity HMC aptamer was used to fabricate an Au nanostructured/carbon paste electrode (Au-NS/CPE). HMC at high blood concentration (hyperhomocysteinemia) can be associated with endothelial cell damage leading to blood vessel inflammation, thereby possibly resulting in atherogenesis leading to ischemic damage. Our proposed protocol was to selectively immobilize the aptamer on the gate electrode with a high affinity to the HMC. The absence of a clear alteration in the current due to common interferants (methionine (Met) and cysteine (Cys)) indicated the high specificity of the sensor. The aptasensor was successful in sensing HMC ranging between 0.1 and 30 μM, with a narrow limit of detection (LOD) as low as 0.03 μM.

High-Performance CMOS Inverter Array with Monolithic 3D Architecture Based on CVD-Grown n-MoS2 and p-MoTe2.

In thiswork, monolithic three-dimensional complementary metal oxide semiconductor (CMOS) inverter array has been fabricated, based on large-scale n-MoS2 and p-MoTe2 grown by the chemical vapor deposition method. In the CMOS device, the n- and p-channel field-effect transistors (FETs) stack vertically and share the same gate electrode. High k HfO2 is used as the gate dielectric. An Al2 O3 seed layer is used to protect the MoS2 from heavily n-doping in the later-on atomic layer deposition process. P-MoTe2 FET is intentionally designed as the upper layer. Because p-doping of MoTe2 results from oxygen and water in the air, this design can guarantee a higher hole density of MoTe2 . An HfO2 capping layer is employed to further balance the transfer curves of n- and p-channel FETs and improve the performance of the inverter. The typical gain and power consumption of the CMOS devices are about 4.2 and 0.11 nW, respectively, at VDD of 1V. The statistical results show that the CMOS array is with high device yield (60%) and an average voltage gain value of about 3.6 at VDD of 1 V. This work demonstrates the advantage of two-dimensional semi-conductive transition metal dichalcogenides in fabricating high-density integrated circuits.

Tuned drop-shape magnetophoretic conductors for controlled single-particle transport in microfluidic chips

In recent years, lab-on-a-chip devices have attracted many researchers due to their numerous advantages, making them suitable for important bioapplications. One of the key challenges in this field is manipulating a group of particles and cells at single-particle resolution. Different techniques have been proposed to tackle this challenge; however, none of them offer the controllability and scalability required in most bioapplications. Recently, drop-shape magnetophoretic circuits have been introduced as an advanced technique for the precise transport of a great number of particles simultaneously. However, in moving along the magnetic track, the particles experience a sudden jump from one magnet to the next one, which may not be in a highly controlled fashion and can be problematic. To overcome this issue, in the current work, we introduce a new design equipped with a tuning gate electrode added to the blind spots of the magnetophoretic conductor. This design transports the particles in a tri-axial magnetic field, with a vertical bias field that reduces the attraction force between particles and inhibits the particle cluster formation. We study the effect of straight and curved current-carrying gates and show that they positively affect the resulting magnetic energy. Based on our finite element method, we found the curved gate offers controlled smooth particle transport at lower electrical currents. We fabricate the proposed chip based on this design and show that the experimental results agree well with the simulation predictions. The introduced design enhances the reliability of the magnetophoretic circuits operating in a tri-axial magnetic field and makes them good candidates for fundamental applications in single-cell biology and medicine.

Design and sensitivity estimation of linear graded work function gate electrode hetero junction vertical TFET biosensor

Design and sensitivity estimation of linear graded work function gate electrode hetero junction vertical TFET biosensor

Sensitivity and Stability Analysis of Double-Gate Graphene Nanoribbon Vertical Tunnel FET for Different Gas Sensing

Sensing and detecting gases are crucial from the application point of view. The essential condition for present-time gas sensors is light, compact, less power dissipation, highly sensitive, thermally stable, and a good selection regards several gases. Due to the significant potential and modulation of the energy bandgap, two-dimensional material has recently attracted researchers attention. Graphene nanoribbon (GNR) is one of the candidates from the two-D material; it is extracted from the strip of one-dimensional graphene material, which can be a suitable contender for gas sensing devices. Therefore, in this work, the detailed investigation of the gas sensor of various gas has been reported by employing two-dimensional material-based DG-GNR VTFET as a sensor. Different gases, including Oxygen, Ammonia as well as Hydrogen gas, have been scrutinized for sensitivity and stability in several temperature ranges. In the present work, several catalytic metals are utilized in the gate electrode of the proposed device architecture for the different gas sensing applications. The intrinsic physics of the proposed gas sensor has been carried out in detail in the factor of different gas molecules and gas pressure. Finally, the temperature parameter varies to analyze the stability of the proposed device sensor within 200 K–400 K.

High voltage power supply for steady state operation of the neutral beam test facility ELISE

The Neutral Beam Injection (NBI) system of ITER shall provide 33 MW heating power to the plasma for up to one hour by two injectors. The beam lines will be based on large RF-driven sources for negative hydrogen or deuterium ions. The test facility ELISE (Extraction from a Large Ion Source Experiment) at IPP Garching is supporting the ion source development for ITER with an ion source of 1 × 1 m2 (half the size of the ITER source). While plasma operation of ELISE is possible for up to one hour, the extraction and acceleration of a negative ion beam (up to 60 kV) was initially possible only for ≈10 s every ≈150 s with the old power supply. During such pulses the temporal behavior of the co-extracted electrons significantly depends on whether beam extraction is switched on or off. Thus, continuous wave (CW) extraction is mandatory for developing fully ITER relevant operational scenarios and recently, a steady state power supply for beam extraction has been installed at ELISE. This power supply consists of two stages connected in series: a first stage with 12 kV / 70 A, providing 35 A for the extracted negative ion current, with a 35 A overhead for co-extracted electrons. The second stage of 50 kV / 35 A is used for the further acceleration of only the ions to a total potential of 60 kV. The two stages have an electrical active power of 1.75 MW and 0.84 MW respectively. The power supply operates with pulse step modulation. Bipolar transistors with insulated gate electrodes (IGBT) are used as electrical switches on the DC side. The 50 kV stage consists of 64 modules in series and the 12 kV stage has 24 modules. Both stages are controlled synchronously and must detect breakdowns between the grids in a µs range.

Enhancing the coherence of superconducting quantum bits with electric fields

In the endeavor to make quantum computers a reality, integrated superconducting circuits have become a promising architecture. A major challenge of this approach is decoherence originating from spurious atomic tunneling defects at the interfaces of qubit electrodes, which may resonantly absorb energy from the qubit’s oscillating electric field and reduce the qubit’s energy relaxation time T1. Here, we show that qubit coherence can be improved by tuning dominating defects away from the qubit resonance using an applied DC-electric field. We demonstrate a method that optimizes the applied field bias and enhances the average qubit T1 time by 23%. We also discuss how local gate electrodes can be implemented in superconducting quantum processors to enable simultaneous in situ coherence optimization of individual qubits.

Solid‐State Homojunction Electrochemical Transistors and Logic Gates on Plastic

AbstractOrganic electrochemical transistors (OECTs) have attracted significant attention due to their unique ionic–electronic charge coupling, which holds promise for use in a variety of bioelectronics. However, the typical electronic components of OECTs, such as the rigid metal electrodes and aqueous electrolytes, have limited their application in solid‐state bioelectronics that requires design flexibility and a variety of form factors. Here, the fabrication of a solid‐state homojunction OECT consisting of a pristine polymer semiconductor channel, doped polymer semiconductor electrodes, and a solid electrolyte is demonstrated. This structure combines the photo‐crosslinking of all of the electronic OECT components with the selective doping of the polymer semiconductor. Three Lewis acids (gold (III) chloride (AuCl3), iron (III) chloride (FeCl3), and copper (II) chloride (CuCl2) ) are utilized as dopants for the metallization of the polymer semiconductor. The AuCl3‐doped polymer semiconductor with an electrical conductivity of ≈100 S cm−1 is successfully employed as the source, drain, and gate electrodes for the OECT, which exhibited a high carrier mobility of 3.4 cm2 V−1 s−1 and excellent mechanical stability, with negligible degradation in device performance after 5000 cycles of folding at a radius of 0.1 mm. Homojunction OECTs are then successfully assembled to produce NOT, NAND, and NOR logic gates.

Magnetic carbon gate electrodes for the development of electrolyte-gated organic field effect transistor bio-sensing platforms

An electrolyte-gated organic field-effect transistor that uses a magnetic carbon gate electrode to collect magnetic nanoparticles properly modified with a bio-receptor is reported as a novel platform to develop sensitive bio-sensors.

Evaluation and bioparticle density correlation analysis of extended gate HEMT sensors for biological detection from microscopic view

In this letter, we focus on the relationship between modification bioparticle density (N) and biological regulation ability in extended gate HEMT (EG-HEMT) biosensors. By analyzing, we demonstrate that under the same gate electrodes size (S g) and concentration, N is exponentially related to the area of sensing regions (y) and has fixed exponential magnification −0.65 ± 0.05. This formula had been demonstrated to have perfect universality when testing protein and small molecules. Finally, we apply N to the structural design of EG-HEMT biosensors and projected that 10 y structure has both high biological regulation ability of biosensors and efficient utility of chips.