Drain Current Decreases Research Articles

CJFET Differential Pairs’ Constructions and Characteristics for Design of Cbicjfet Differential Amplifiers and Differential Difference Amplifiers’

We have developed technology and construction solutions system to increase differential pairs (DP) of JFet with p- and n-channels identity, which are included into silicon complementary bipolar process of SPE “Pulsar” (Moscow). The possibility of creating several types of JFet DPs within the process is shown. The paper presents the results of experimental studies of two types of DP JFet designs with p- and n-channels for the spread of gate-source voltage ΔVGS depending on the drain current and drain-source voltage. The main features of the first design of p-channel JFets were the following: formation of drain/source area due to passive base of npn-transistor and deep collector areas for pnp-transistor; channel formation based on p-layer collector of pnp-transistor; formation of bottom gate using p+ buried layer; top gate formation due to active base and polysilicon emitter of npn-transistor. A feature of the second JFet design was top gate formation due to passive base. The designs of the first and second types of n-channel Jfet were formed similarly, taking into account the replacement of the applied areas of bipolar transistors with opposite ones in the type of conductivity. It was found that with increasing drain current ΔVGS decreases, and with increasing drain-source voltage ΔVGS at high currents increases for DP based on p-channel JFet with the first type of design. The maximum difference ΔVGS was in the range of 5–80 mV for a given differential pair JFet with a p-channel. On plots for DP p-channel JFet with the second type design a significantly lower voltage spread ΔVGS was shown: for example, for the drain current ID = 50 μA the voltage spread ΔVGS did not exceed 10 mV. In this case the voltage spread ΔVGS practially did not depend on drain-source voltage in contrast to differenctial pair of the first type. The second type JFet n-channel differential pairs like for the DP p-channel JFet provided lower spread values in comparison with the first type design: ΔVGS reached values of 5-20 mV. Moreover, for the design of the second type, a significantly weaker effect of the drain-source voltage on ΔVGS was observed at high current densities. The developed designs of differential pairs based on p- and n-channel JFet are recommended for use in organizing the production of CBiCJFet analog circuits, including operations at low temperatures.

Comparative study of Au and Ni/Au gated AlGaN/GaN high electron mobility transistors

This paper presents the electrical comparison of Au and Ni/Au gated HEMT devices and diodes. Au Schottky diodes on an AlGaN/GaN heterostructure exhibit better electrical performance in comparison to conventional Ni/Au diodes with an improved Schottky barrier height (SBH) and lower reverse leakage current. The SBH extracted from I-V for Au and Ni/Au is 1.29 eV and 0.74 eV, respectively. Au Schottky contacts on GaN have a better ideality factor of 1.55 than Ni, which is 1.61. Capacitance-voltage measurement revealed a positive shift in threshold voltage in the case of Au diodes with a reduced capacitance value with respect to Ni/Au diodes. This decrease in threshold and capacitance indicates a decrease in the 2DEG carrier concentration. The decrease in the 2DEG carrier concentration is consistent with three terminal device measurements. Despite a small decrease in drain current (8%), the Au gated HEMT devices have shown an improved subthreshold slope (13%) and nearly 4 order improvement in the ION/IOFF ratio than Ni/Au gated HEMTs. Pulse IV characterization has indicated that gate lag and drain lag have no major changes with respect to gate metal, whereas current collapse increases for high work function metals.

Temperature based analysis of 3-step field plate AlGaN/GaN HEMT using numerical simulation

In this work, temperature based instability of the 3-step field plate (FP) AlGaN/GaN HEMT has been explored using ATLAS TCAD. DC performance characteristics such as: drain current, trans-conductance and Ion/Ioff ratio at different temperatures (ranging from 300 K to 500 K) and GaN channel thicknesses (from 150 nm to 500 nm) have been investigated. It has been observed that, drain current decreases with rise in temperature with a coefficient of approximately −0.0031 mA μm−1 K−1. Subsequently, impact of temperature on breakdown voltage, electric field, electron temperature and parasitic capacitances has also been investigated. Enhancement in breakdown voltage and reduction in trans-conductance has been observed with rise in temperature for above zero temperature coefficient bias point. Along with temperature variation, impact of GaN channel, AlGaN barrier thickness and mole fraction of aluminium concentration has also been studied and it is seen that breakdown voltage and Ion/Ioff increases for thinner channel and barrier thickness.

Effect of defects properties on InP-based high electron mobility transistors**Project supported by the National Natural Science Foundation of China (Grant Nos. 11775191, 61404115, 61434006, and 11475256), the Development Fund for Outstanding Young Teachers in Zhengzhou University of China (Grant No. 1521317004), and the Doctoral Student Overseas Study Program of Zhengzhou University, China.

The performance damage mechanism of InP-based high electron mobility transistors (HEMTs) after proton irradiation has been investigated comprehensively through induced defects. The effects of the defect type, defect energy level with respect to conduction band ET, and defect concentration on the transfer and output characteristics of the device are discussed based on hydrodynamic model and Shockley–Read–Hall recombination model. The results indicate that only acceptor-like defects have a significant influence on device operation. Meanwhile, as defect energy level ET shifts away from conduction band, the drain current decreases gradually and finally reaches a saturation value with ET above 0.5 eV. This can be attributed to the fact that at sufficient deep level, acceptor-type defects could not be ionized any more. Additionally, the drain current and transconductance degrade more severely with larger acceptor concentration. These changes of the electrical characteristics with proton radiation could be accounted for by the electron density reduction in the channel region from induced acceptor-like defects.

Detection and Analysis of Extracellular Vesicles in Physiological Salt Environment Using AlGaN/GaN High Electron Mobility Transistor Biosensors

Extracellular vesicles (EVs) have emerged as a research area attracting intense investigation. The enumeration and surface marker analysis of EVs have been conducted using conventional techniques and correlated with incidence and metastasis of various cancers and risk assessment of cardiovascular diseases. With efforts to characterize EVs as specific diseases biomarkers, it is imperative to develop sensitive and robust detection techniques to monitor the presence of EVs in physiological fluids. Previously, we demonstrated direct protein detection from physiological fluids using high field modulated field effect transistor (FET) biosensor. In the present work, we have utilized antibody functionalized AlGaN/GaN high electron mobility transistor (HEMT) to capture EVs from high salt environment (1X PBS) and resulting change in electrical response of the sensor has been correlated with the concentration of EVs. The unique high field modulation applied to the sensor facilitates target detection overcoming Debye screening. Our sensor can achieve better sensitivity (detection limit of 107 EVs/mL) than the conventional technologies used for EV detection such as nanoparticle tracking analyzer. Furthermore, our sensor methodology can also be used to determine the surface markers present in the captured EVs. In our sensor, when EVs are captured by the immobilized anti-CD63, the solution capacitance varies as the applied potential drops across the solution, thereby modulating the HEMT drain current. When we employ a secondary antibody such as anti-CD9 to bind with CD9 which is abundantly present on the exosomal membrane, the impedance increases, resulting in more potential drop across the solution and therefore, a decrease in drain current (Figure 1). The results in Figure 1 indicate that our sensor can perform EV enumeration and exosomal surface marker analysis to establish a comprehensive diagnostic model for EVs in physiological fluids. Figure 1

Detection and Analysis of Extracellular Vesicles in Physiological Salt Environment Using AlGaN/GaN High Electron Mobility Transistor Biosensors

In the present work, we have utilized antibody functionalized AlGaN/GaN high electron mobility transistor (HEMT) to capture EVs from high salt environment (1X PBS) and resulting change in electrical response of the sensor has been correlated with the concentration of EVs. The unique high field modulation applied to the sensor facilitates target detection overcoming Debye screening. Our sensor can achieve better sensitivity (detection limit of 107 EVs/mL) than the conventional technologies used for EV detection such as nanoparticle tracking analyzer. Furthermore, our sensor methodology can also be used to determine the surface markers present in the captured EVs. In our sensor, when EVs are captured by the immobilized anti-CD63, the solution capacitance varies as the applied potential drops across the solution, thereby modulating the HEMT drain current. When we employed a secondary antibody such as anti-CD9 to bind with CD9 which is abundantly present on the exosomal membrane, the impedance increases, resulting in more potential drop across the solution and therefore, a decrease in drain current. The results indicate that our sensor can perform EV enumeration and exosomal surface marker analysis to establish a comprehensive diagnostic model for EVs in physiological fluids.

Gas sensing characteristics of the FET-type gas sensor having inkjet-printed WS2 sensing layer

This paper investigates the gas sensing characteristics of the MOSFET-type sensor having an inkjet-printed WS2 sensing layer. The drain current of the gas sensor increases when NO2 gas is injected into the test chamber since NO2 gas is an oxidizing gas that extracts electrons from the sensing layer. On the contrary, the drain current decreases when H2S gas is injected into the test chamber since H2S gas is a reducing gas that donates electrons to the sensing layer. In both cases, the change of the drain current increases as the gas concentration increases. However, for other gases (NH3 and CO2), the gas sensor has a small change of the drain current. The responses of the gas sensor to 10 ppm NO2, H2S, NH3, and CO2 gases are 15.20%, 7.18%, 1.66%, and 3.02%, respectively. Therefore, the WS2 sensor has a high selectivity for NO2 gas among the four target gases.

Temperature-Dependent Transport in Ultrathin Black Phosphorus Field-Effect Transistors.

We studied the temperature-dependent transport properties of ultrathin black phosphorus (BP). We present measurements of BP Schottky barrier (SB) metal-oxide-semiconductor field-effect-transistors (MOSFETs) with various channel lengths, constructed from a single BP sample with nanoscale uniformity in thickness and width. The electrical characterization reveals a reversal in the temperature dependence of drain current as a function of gate voltage. This reversal indicates a transition in the charge conduction limiting mechanisms as the device is swept from the off-state into the on-state. In the off-state, charge transport is limited by thermionic emission over the energy barriers at the source/drain SB contacts, and drain current increases with temperature. In the on-state, carriers can easily tunnel across the SB at the contacts, and charge transport is limited by scattering in the channel. As a result, drain current decreases with temperature in the on-state, as scattering increases with temperature. Using Landauer transport theory, we derive a closed-form expression for thermionic emission current in SB-MOSFETs with two-dimensional channels. We use this expression to extract the SB height at metal contact interface with BP and demonstrate the impact of scattering on the extraction. We then use a comprehensive BP SB-MOSFET model to analyze on-state current as a function of temperature and demonstrate the effects of charged impurity and phonon scattering on the transport properties of BP through extractions of mobility at fixed carrier density.

Vertical GaN n-channel MISFETs on ammonothermal GaN substrate: Temperature dependent dynamic switching characteristics

Switching of GaN-based vertical-trench gate MISFET on ammonothermal n-type GaN substrate are studied as a function of temperature. Pulsed on-state IV characterization revealed three unexpected independent effects. First, drain current increases with temperature, although electron mobility decreases with temperature. Second, drain current decreases with pulse length, which cannot be explained by heating. Third, dynamic Ron increases with off-state drain bias, which usually is considered as an issue of lateral GaN HFETs only. The drain current temperature dependence is most likely dominated by the low electron mobility in the inversion layer beneath the gate. The field effect channel mobility is estimated as < 10 cm2/V s and can thus be considered as trap limited and thermally activated, Ron decreases from 133 Ω mm at 20 °C to 62 Ω mm at 110 °C. Longer on-state pulses lead to negative charging of the ALD-Al2O3 gate oxide and shift the threshold voltage (DC-Vth ~8 V) positively. With the maximum applicable Vgs = 10 V, the drain current is not saturated yet and Ids thus drops by a factor 2 when increasing the on-state pulse width from 0.2 µs to 20 µs due to the Vth-shift. The observed 10-times dynamic Ron increase with off-state drain bias up to 30 V can be related to possible charging mechanism in the gate oxide as well. Activation energies for different off-state stress voltage are ranged linear between 0.08 eV and 0.26 eV for drain bias stress of Vds = 0 V and 30 V respectively.

Total ionizing dose influence on proton irradiated triple gate SOI Tunnel FETs

This paper reports an analysis of radiation effects on triple gate SOI tunnel FETs from a total ionizing dose point of view, based on measurements and TCAD simulations. Devices with different dimensions were exposed to a dose of 1 Mrad(Si) generated by a 600 keV proton radiation source. It was possible to notice a drain current decrease for irradiated devices that reduces with increasing channel length and gate bias. To explain this behavior, the influence of positive charges at front and back interfaces generated by the cumulative exposure to radiation was analyzed, as well as devices’ internal characteristics for such operation conditions. This analysis is based on the competition between a high channel resistance present in longer devices and the TFET drain current reduction due to the irradiation.

Structural Modification of Organic Thin-Film Transistors for Photosensor Application

We investigated the light response characteristics of bottom-gate/top-contact organic TFTs fabricated using pentacene and polystyrene as an organic semiconductor and a polymeric insulator, respectively. The pentacene TFT with overlaps (50 μm) between the source and gate electrodes as well as between the drain and gate electrodes exhibited negligible hysteresis in its transfer characteristics upon reversal of the gate voltage sweep direction. When the TFTs were structurally modified to produce an underlap structure between the source and gate electrodes, clockwise hysteresis and a drain-current decrease were observed, which were further augmented by increasing the gate underlap (from 30 μm to 50 μm and 70 μm). Herein, these results are explained in terms of space charge formation and accumulation capacitance reduction. Importantly, we found that space charges formed under the source electrode contributed to the drain currents via light irradiation through the underlap region. Under constant bias conditions, the TFTs with gate underlap structures thus exhibited on-state drain current changes in response to light signals. In our study, an optimal photosensitivity exceeding 11 was achieved by the TFT with a 30 μm gate underlap. Consequently, we suggest that gate underlap structure modification is a viable means of implementing light responsiveness in organic TFTs.

Soft-type trap-induced degradation of MoS2 field effect transistors

The practical applicability of electronic devices is largely determined by the reliability of field effect transistors (FETs), necessitating constant searches for new and better-performing semiconductors. We investigated the stress-induced degradation of MoS2 multilayer FETs, revealing a steady decrease of drain current by 56% from the initial value after 30 min. The drain current recovers to the initial state when the transistor is completely turned off, indicating the roles of soft-traps in the apparent degradation. The noise current power spectrum follows the model of carrier number fluctuation–correlated mobility fluctuation (CNF–CMF) regardless of stress time. However, the reduction of the drain current was well fitted to the increase of the trap density based on the CNF–CMF model, attributing the presence of the soft-type traps of dielectric oxides to the degradation of the MoS2 FETs.

Anomalous Source-Side Degradation of InAlN/GaN HEMTs Under High-Power Electrical Stress

The electrical degradation of InAlN/GaN high-electron-mobility transistors for millimeter-wave applications has been examined under simultaneous high ${V}_{\text {DS,stress}}$ and high ${I}_{{D\text {stress}}}$ electrical stress. Besides a drain current decrease and a positive threshold voltage shift, the creation of an anomalous source-side gate leakage path has been identified. We attribute this to high electric-field induced trap generation in the AlN layer directly under the gate edge on the source side. The resulting increase in gate leakage further exacerbates the degradation of the gate diode. In addition, we postulate that high-power stress leads to significant device self-heating that causes gate sinking and leads to a permanent positive threshold voltage shift and drain current degradation.

Detection of ammonia at low concentrations (0.1–2 ppm) with ZnO nanorod-functionalized AlGaN/GaN high electron mobility transistors

AlGaN/GaN high electron mobility transistors with ZnO nanorod functionalized gates were used for detecting NH3 in the concentration range of 0.1–2 ppm balanced with air at ambient temperatures from 25 to 300 °C. A decrease in the high electron mobility transistor drain current was observed for exposure to the NH3-containing ambients, indicating an increase in negative charge at the heterointerface. The detection sensitivity increased monotonically with ammonia concentration at all temperatures, from 0.28% (25 °C) and 3.17% (300 °C) for 0.1 ppm to 1.32% (25 °C) and 13.73% (300 °C) for 2 ppm for a drain–source voltage of 1 V. The latter condition is attractive for low power consumption. The sensitivity was also a function of applied voltage and was generally higher in the linear region of the current–voltage characteristic of the transistor. The activation energy of the sensitivity was 0.09 eV, and the sensors showed no response to O2 (100%), CO2 (10%), CO (0.1%), CH4 (4%), and NO2 (0.05%) under the same detection conditions as used for the NH3. The response was less than 1 s, and recovery times were of order ∼53 s at 25 °C.

Effects of Gd2O3 Gate Dielectric on Proton-Irradiated AlGaN/GaN HEMTs

AlGaN/GaN high electron mobility transistors (HEMTs) and MOS-HEMTs using Gd2O3 as gate dielectric were irradiated with 2-MeV protons up to fluence of $1 \times 10^{15}$ cm−2. Results showed that proton irradiation causes a strong degradation in the Schottky gate devices, featured by more than three orders of magnitude increase in reverse leakage current, a 30% decrease in maximum drain current, and the same percentage of increase in ON-resistance, respectively. Scanning transmission electron microscopy showed that radiation induced a diffusion of Ni into Au in the gate and void formation, degrading the transistors’ characteristics. The Gd2O3 gate dielectric layer prevented this diffusion and void formation. MOS-HEMTs with Gd2O3 gate dielectric show 50% less decrease of performance under proton irradiation than Schottky gate HEMTs (conventional HEMTs). The trapping effects of Gd2O3 gate layer before and after irradiation are also discussed.

Impact of Recess Etching on the Temperature-Dependent Characteristics of GaN-Based MIS-HEMTs With Al2O3/AlN Gate-Stack

This paper studied the recess-etching effects on the temperature-dependent characteristics of AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) with Al2O3/AlN gate-stack. The 12.6 nm recess-etching resulted in voltage shift of capacitance-voltage curves by 2.4 V, improved peak field-effect mobility ( $\mu _{\text {FE}})$ from 1906 to 2036 cm2/ $\text{V}\cdot \text{s}$ , and increased peak transconductance ( ${g}_{\text {max}})$ from 272 to 353 mS/mm. The temperature-dependent measu-rement from 298 to 473 K showed decrease in maximum drain current, ${g}_{\text {max}}$ , and $\mu _{\text {FE}}$ for both devices with and without recess etching, attributed to thermal electron emission and carrier depletion effects. Recess etching did not degrade the thermal stability of carrier distribution and the transport properties. Temperature-dependent $\mu _{\text {FE}}$ analysis revealed that optical phonon scattering dominated the transport mechanism of Al2O3/AlN/ AlGaN/GaN MIS-HEMTs. Optical phonon energy of 74 and 77 meV were obtained for the devices with and without recess etching, respectively.

Role of two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistor (HEMT) ON-state degradation

We have investigated the influence of the two-dimensional electron gas (2DEG) in AlGaN/GaN high electron mobility transistors (HEMTs) on their reliability under ON-state conditions. Devices stressed in the ON-state showed a faster decrease in the maximum drain current (IDmax) compared to identical devices stressed in the OFF-state with a comparable electric field and temperature. Scanning electron microscope (SEM) images of ON-state stressed devices showed pit formation at locations away from the gate-edge in the drain-gate access region. Cross-sectional transmission electron microscope (TEM) images also showed dark features at the AlGaN/SiN interface away from the gate edge. Electron energy loss spectroscopy (EELS) analysis of the dark features indicated the presence of gallium, aluminum and oxygen. These dark features correlate with pits observed in the SEM micrographs. It is proposed that in addition to causing joule heating, energetic electrons in the 2D electron gas contribute to device degradation by promoting electrochemical oxidation of the AlGaN.

A Disposable paper breathalyzer with an alcohol sensing organic electrochemical transistor.

Breathalyzers estimate Blood Alcohol Content (BAC) from the concentration of ethanol in the breath. Breathalyzers are easy to use but are limited either by their high price and by environmental concerns, or by a short lifetime and the need for continuous recalibration. Here, we demonstrate a proof-of-concept disposable breathalyzer using an organic electrochemical transistor (OECT) modified with alcohol dehydrogenase (ADH) as the sensor. The OECT is made with the conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), and is printed on paper. ADH and its cofactor nicotinamide adenine dinucleotide (NAD+) are immobilized onto the OECT with an electrolyte gel. When the OECT-breathalyzer is exposed to ethanol vapor, the enzymatic reaction of ADH and ethanol transforms NAD+ into NADH, which causes a decrease in the OECT source drain current. In this fashion, the OECT-breathalyzer easily detects ethanol in the breath equivalent to BAC from 0.01% to 0.2%. The use of a printed OECT may contribute to the development of breathalyzers that are disposable, ecofriendly, and integrated with wearable devices for real-time BAC monitoring.

Force-pad made from contact-electrification poly(ethylene oxide)/InSb field-effect transistor

A contact electrification field-effect transistor (CE-FET) is first made from poly(ethylene oxide)/InSb/PET(polyethylene terephthalate) on the flexible force-pad application. The CE-FET operates on a unique principle that relies on the triboelectric potential difference that is established between the two tribo-surfaces, to induce an inner electrical signal by utilizing the external frictional force. Such a signal is able to modulate the carrier transport characteristics in the FET and is self-generated to have the same effect as applying a gate signal. The traditional gate electrode in the FET is replaced by an individually mobile aluminum and a polytetrafluoroethene (PTFE) electrode to serve as a positive and negative gate voltage, respectively. The n-type rich indium (In) InSb thin film is then used as a conduction channel in the CE-FET. When the PTFE film acted as a mobile gate electrode to progressively contact the PEO surface, the drain current was increased from 6 to 12μA by increasing the distance (d) between the PEO and the PTFE surfaces in the range from 0 to 80μm. In contrast, when the Al film was used as a mobile electrode to gradually contact the PEO surface, the corresponding drain current decreases from 7μA to 1.5μA, while increasing the corresponding distance from 0 to 80μm, respectively. Thus, the characteristic of the CE-FET has established an enhancement and depletion mode in the InSb conduction channel when the mobile electrodes of the PTFE and aluminum films were mechanically attached to the PEO surface, respectively. The CE-FET InSb is highly reliable and sensitive, which thereby opens up a new research field on the applications of the force pads.

The effect of random dopant fluctuation on threshold voltage and drain current variation in junctionless nanotransistors

We investigate the effect of dopant random fluctuation on threshold voltage and drain current variation in a two-gate nanoscale transistor. We used a quantum-corrected technology computer aided design simulation to run the simulation (10000 randomizations). With this simulation, we could study the effects of varying the dimensions (length and width), and thicknesses of oxide and dopant factors of a transistor on the threshold voltage and drain current in subthreshold region (off) and overthreshold (on). It was found that in the subthreshold region the variability of the drain current and threshold voltage is relatively fixed while in the overthreshold region the variability of the threshold voltage and drain current decreases remarkably, despite the slight reduction of gate voltage diffusion (compared with that of the subthreshold). These results have been interpreted by using previously reported models for threshold current variability, load displacement, and simple analytical calculations. Scaling analysis shows that the variability of the characteristics of this semiconductor increases as the effects of the short channel increases. Therefore, with a slight increase of length and a reduction of width, oxide thickness, and dopant factor, we could correct the effect of the short channel.