Current Id Research Articles

Stressor SiNx contact etch stop layer (CESL) technology and its application in nano-scale transistors

The high stress SiNx thin film deposition technology is widely used in nano-scale transistor structure to induce strain and improve the carrier transport in the channel region. In this work, the synthesis and process of high tensile stress SiNx thin films have been studied. High tensile stress SiNx thin film is obtained by multiple treatment of N2 plasma. The optimized SiNx films was integrated into the 26 nm transistors and found that the driving current Idsat was improved by 27%.

The Development of a New Ion Versus Log(Ig) Plot to Characterize Depletion-Mode High Electron Mobility Transistors with the Insertion of a Very Thin Evaporated Al Layer to AlGaN/GaN High Electron Mobility Transistors as an Example

Previously, we showed that the Id_on vs. log Id_off plot can be used to characterize silicon-based enhancement-mode MOS transistors for both p-channel and n-channel [1]. AlGaN/GaN high electron mobility transistors (HEMTs) have attracted world-wide interest for microwave power transistor applications. There are two kinds of AlGaN/GaN HEMTs: depletion-mode and enhancement-mode AlGaN/GaN HEMTs. In general, depletion-mode AlGaN/GaN HEMTs are more common. For depletion-mode devices with the source at 0 V, even though the gate voltage may be close to zero, the gate leakage current increases with the increase of the drain voltage and can be significant because of a large drain voltage. Thus the gate leakage current may limit the maximum drain voltage and thus the RF power output of the device. For depletion-mode high electron mobility transistors (HEMTs), it can be easily imagined that both the on current (Ion) and the gate leakage current (Ig) will be increased by using a low work function metal as gate metal. Thus the drain on current (Id_on) and the gate leakage current (Ig) alone will not be a good criterion to judge the quality of depletion-mode HEMTs. In this paper, we would like to propose the application of a new Id_on vs. log Ig plot to characterize depletion-mode HEMTs. In the literature, a lot of various approaches have been proposed to cut down the gate leakage current. Recently, Nanjo et al. proposed to use a thin Al layer inserted between AlGaN and the Schottky metal gate to reduce the gate leakage current [2]. The advantage of this approach was subsequently confirmed by Selvaraj and Egawa [3]; however, they emphasized on the increase of the drain current instead of the reduction in the gate leakage current. It is natural to wonder how Al insertion can ever increase the drain current. Hence, the physics behind this approach is not yet clear. In this paper, we will also propose our theory regarding the physics of Al gate for AlGaN/GaN HEMT’s. With the help of this new plot, the superiority of the sample with Al/Ni/Au gate compared to the control sample with Ni/Au gate can be easily seen because the on current is higher for the same gate leakage current.As shown in Fig. 1, it can be easily shown that the Al insertion significantly improves the device for the same gate leakage current. According to theory, the Schottky barrier height φb is given by φb = φm - χs, where φm and χs are the metal work function and the electron affinity of the semiconductor. It is known that the work function of Al is significantly lower than that of Ni. It can be easily predicted that AlGaN/GaN HEMT with Al gate should have much larger gate leakage current compared to that with Ni gate. In fact, this was experimentally observed by us if the Al was evaporated rapidly during sample deposition. Our explanation of the advantage of Al insertion was that there was residual water vapor present in the vacuum chamber during electron beam evaporation [4]. According to Kordos et al. [5], the electron mobility of the 2-D electron gas at the AlGaN/GaN interface can be improved by a thin layer of Al2O3 on top of AlGaN/GaN. This experimental observation was also reported by Liu et al. [6]. It can be easily imagined that the presence of a thick layer of Al2O3 on top of AlGaN/GaN will degrade the performance of AlGaN/GaN HEMT because the distance between the metal gate and the AlGaN/GaN interface becomes bigger. However, when the thickness of the Al2O3 layer is small enough, the improvement of the electron mobility will be more significant than the degradation due to the increase of the distance between the metal gate and the AlGaN/GaN interface, resulting in the improved performance of the AlGaN/GaN HEMT.

Influence of the Biomaterial Thickness in a Dielectrically Charged Modulated Fringing Field Bio-Tunnel-FET Device

The biosensor market is expected to increase more than 40% in 5 years ( 2019 to 2024) due to the versatile of these devices (1). Many research groups are studying new types and optimizations of these devices and the tunnel field-effect transistors (TFET) have attracted the interest due to the many advantages of these devices (2).Figure 1 shows the Bio-TFET cross section which has been simulated with TCAD Sentaurus (3). The proposed device has a gate length (LG), equivalent gate oxide thickness (tox) and channel silicon thickness (tSi) of 40 nm, 1 nm and 10 nm. The drain underlap (LUD) is variable in the range of 1 to 100 nm. The uniform doping profile of the device consists of a source and drain doping concentration of 1020 atom/cm3 of boron and arsenic, respectively. An intrinsic channel with 1015 atom/cm3 of boron. The gate electrode has a workfunction of 4.7 eV. The main models incorporated in the simulation were the bandgap narrowing (BGN), Shockley Read Hall recombination (SRH) and the nonlocal band-to-band tunneling (BTBT). In the drain underlap region is deposited a biomaterial for biosensing purposes. This material has a dielectric constant (k, where ε=k*ε0) of 1 (air), 2.1 (Streptavidin), 3.57 (APTES), 8 (Anti-Iris antibody) and 10 (Isoquinoline) (4).Figure 2 shows the Bio-TFET transfer characteristics. The ambipolar region is a parasitic tunneling current that occurs for negative gate bias (VG) for nTFET at drain to channel region. In order to decrease this effect a drain underlap (LUD) is performed at the device (5). However, when the biomaterial dielectric constant (k) increases, the ambipolar current also increases orders of magnitude, meaning that the device is very susceptible to k variation in the biomaterial region and can be used for biosensing of different types of biomolecules with a distinct k. In order to quantify the influence of change in k in the biomaterial region the equation in terms of ID: Sensitivity = ΔID/ID(Ref.) was used. Where ΔID represents the difference between the drain current of biosensing (output), e.g., the drain current with the presence of biomaterial ID(Bio) and the drain current of reference ID (Ref.) (input), e.g., drain current without biomaterial ID (k=1) . Both for a fixed value of gate voltage (VG = -2 V) in the ambipolar region. Fig.3 shows the sensitivity of the device as a function of LUD for different k values. The maximum sensitivity occurs for a LUD = 30 nm for all range of k values. The sensitivity increases for higher k as reported in (6). Another parameter that is important for sensing is the dimension of the target. Many biomolecules have different types, e.g., spherical, ellipsoidal or elongated (7). Therefore, the study of the parameter is fundamental for the functional operation of the device. In Fig.4 the sensitivity is analyzed as a function of biomaterial thickness (tBio) for a fixed value of LUD=30nm. With the rising of tBio and k the sensitivity increases, i.e., exceeding 2 orders of magnitude comparing tBio = 10nm and tBio = 30 nm for k = 10. This increment on sensitivity is due to the tunneling length lowering, as can be noticed in Fig.5. The tunneling length decrease from 5.7 nm (tBio= 10 nm) to 9.5 nm (tBio = 30 nm), both for k = 10 and fixed energy of - 1 eV. The lowering of the tunneling length increases the ambipolar current ID(Bio) that enhances the sensitivity of the device. An important consideration for the biosensing process is the charge on the biomaterial that affect the tunneling current and therefore affect the sensitivity of the device. In Fig. 6, the sensitivity is studied as in the function of positive fixed charges in the range of 1010 to 1012 cm-2. The sensitivity increases for thicker values of tBio. This is due to the higher effect of the fringing field in the region. As tBio increase the effect of fringing field increases in the biomaterial region and as consequence, the device becomes more sensible with the presence of charges.The study of charges and biomaterial thickness in a dielectrically modulated fringing field Bio-TFET was performed in this work. The device shows high sensitivity with the increase of tBio in the range studied in this work. Although, the effect of fixed charges is more notable for thicker tBio. Then, the tBio thickness shows a high impact in the sensing of the device. Figure 1

Errors of Integrated Hydrogen Sensors Based on FETs with Structure Pd (Ag)–Ta2O5 –SiO2 –Si

Introduction There are a lot of hydrogen sensors commercially available or in development, which can be used in the environmental and fire-explosion safety monitoring devices [1]. Among solid-state gas sensitive elements, the capacitor and transistor elements based on metal-insulator-semiconductor (MIS) structures possess the best compatibility with the integrated circuits’ elements. Therefore, such sensitive elements seem promising to develop the integrated hydrogen sensors and gas analysis microsystems-on-chip. The sensors based on MIS-devices (MIS-capacitors and field-effect transistors called as FETs) have been studied by many investigators. A great contribution to the developments of gas-sensitive MIS-devices has been made by the researchers at Linköping University [2] since their pioneering work [3]. The researchers at NRNU MEPhI developed the MIS sensors based on structures Pd (or Pt)-SiO2-Si, Pd/Ti-SiO2-Si, Pd (or Pt)-Ta2O5-SiO2-Si. The best characteristics belong to the integrated cells containing on silicon chip two gas-sensing elements (Pd-resistor and FET with structure Pd(Ag)-Ta2O5-SiO2-Si), temperature sensor and heater. Effects of electrical modes, chip temperature and radiation on the performance of these sensors were studied in previous works (e.g., [4] – [6]). However, sensors’ errors of were not investigated. The motivation of this work is to estimate errors and its components of FET-based hydrogen sensors, using the experimental data and the models proposed for calculation of sensors’ errors. Experimental technique and results The layout of sensor chip, simplified wiring diagrams of elements and parameters of FET are presented in Figure 1 and in Table 1. The n-channel FET element based on Pd(Ag)-Ta2O5-SiO2-Si (1) structure was fabricated on single chip together heater-resistor (2) and with temperature sensor (3) by means of conventional n-MOS-technology using laser evaporation Pd(Ag)-films. The Pd(Ag)-resistor was not investigated because it was previously shown that it has worse characteristics than FET. The measuring circuit provides the constant drain current ID (0.1 mA) and source-drain voltage VD (0.2 V), and the output voltage V is the gate voltage VG . The chip temperature T being equal to (130 ± 2 °С) was supported by the temperature-stabilization circuitry using on-chip thermo-sensor and heater. Five sensors with similar characteristics were selected (dispersion of initial output voltage V 0 is not more than 10%). There were repeatedly measured hydrogen responses of sensors for different concentrations Ci (e.g., ordinary j-cycle in Figure 2a). The model’s parameters ΔVCM and k of the function ΔVC (C) based on the approximation of the averaged values of the experimental points ΔVCi were determined as in [7] (Figure 2b). Averaged values of FET’s parameters in Table 1, values of Vai (Ci ), values of ΔVCi (Ci ) and variation indices θ Vi (Ci ), presented in Table 2, were calculated using Equations (1). Modeling of errors and discussion To estimate errors of FET-based sensors there were proposed general and numerical models of V(D,C), hydrogen sensitivities Si and Sd , absolute ΔC and relative errors δC, the maximum absolute error Δ(V) of the output voltage V, which are given by Equations (2) – (7). According to (3), the component V 0 of model V (D,C) depend on primary voltage V 00, the initial time drift ΔV 0t (t) and the drift ΔV 0(D) associated with the total hydrogen dose D = ∫C(t)dt, and as errors of “zero”, can be compensated by calibrating the sensor measuring circuit. Value V 00 depends on VT 0, ID and b (3). According to models the measurement errors depend on the instrumental errors of etalon concentration ∆C 0 and of voltage measurement ΔVV , the random errors ΔVai associated with the voltage V variations of various sensors, fluctuations of chip temperature ΔVT [4], of electrical circuits’ parameters ΔVID [5] and additional errors ΔVZ due to the influence of other gases and radiation [6]. Besides, errors depend on hydrogen concentration, sensitivity Sd and total hydrogen dose D. Approximated dependences of relative errors on the concentration for different conditions (e.g., Figure 3) can be used to estimate operating concentration ranges for given δC, and hydrogen sensitivity threshold CT (e.g., as in Table 3). Conclusions The proposed methodology of estimation errors of sensors based on FET with structure Pd(Ag)-Ta2O5-SiO2-Si, using numerical models with parameters determined from experimental hydrogen responses, can be applied to estimate errors of integrated sensors with other types of FETs and measuring circuits.

AlGaN/GaN high electron mobility transistors on diamond substrate obtained through aluminum nitride bonding technology

Transfer technology is now becoming very attractive not only for new technologies such as flexible technology but also for solid state technologies when performances are limited by technological barriers that have to be overcome. In this last context, the transfer of high electron mobility transistors (HEMTs) on diamond substrates represents an opportunity to improve the thermal dissipation when the device operates at high radio frequency power levels. Up to now, the technological process for the transfer of these transistors is not detailed in the literature. In this article, the first demonstration of AlGaN/GaN HEMTs on diamond substrates by transfer technology obtained through sputtered aluminum nitride (AlN) layers bonding at low temperature is reported. Devices are first fabricated on AlGaN/GaN epilayers grown on silicon (Si) substrates. Afterward, AlGaN/GaN thin films with devices are released from the Si growth substrate and transferred at 160 °C onto a diamond substrate thanks to an AlN bonding layer. A full description of the transfer technology and all the technological limits and risks are presented. The transferred device provides a maximum DC drain current density IDS Max of 690 mA mm−1 at VGS = 0 V. Furthermore, a cutoff frequency fT of 85 GHz and a maximum oscillation frequency fMAX of 106 GHz are extracted from S-parameter measurements.

Interface trap-induced negative differential resistance in nMOSFET with floating source

Interface trap can act as the generation center in device to induce a very weak generation current. We observed the negative differential resistance NDR of this generation current ID in nMOSFET with the floating source. It originates from that the generation function of interface trap is enabled and then is shut down in turn as increasing the drain voltage. This change relies on the interaction among the interface trap energy-level and the electron's Fermi-levels of drain and source under the floating source condition. It is found that the peak-to-valley ratio of ID is beyond 30.

High sensitive gas sensor based on vertical graphene field effect transistor

A gas sensor made from graphene vertical field effect transistor (VGr-FET) has been fabricated using graphene as the source electrode, C60 thin film as the semiconductor layer and aluminum thin film as the drain electrode. The on/off ratio of transistor gated by bottom electrode with ionic liquid gel as dielectric layer is derived to be 103 from measured source–drain current Ids. The apparent energy barrier height between the graphene and polycrystalline fullerene was calculated from the model of heterojunction diode I–V response curves. The barrier height φBH was altered by the gating potential vertically applied on graphene sheet, resulting the large on/off ratio of the transistor. The effect of surface adsorption of water vapor, oxygen, ammonia and isoprene gas phase molecules on the Ids was measured. The lower limit of detection (LOD) for ammonia (86 ppb) than that of isoprene (420 ppb) is attributed to the donor nature of ammonia contact with p-type graphene, and the adsorbed donor leads to a corresponding positive gating effect to the VGr-FET. This facile, low cost and quick responsive device shows promise for early diagnose of severe human respiratory diseases.

Temperature Dependent Performance Evaluation and Linearity Analysis of Double Gate-all-around (DGAA) MOSFET: an Advance Multigate Structure

Multi-gate devices such as double gate, FinFET and Gate-All-Around (GAA) are potential candidates to achieve the performance expected by semiconductor association. This paper presents an analog/RF performance and linearity distortion analysis for an advance multigate structure named Double Gate-All-Around (DGAA) MOSFET. Temperature dependent characteristics of the DGAA MOSFET have also been investigated in detail from 200 K to 400 K. A comparative analysis between Gate-All-Around (GAA) and DGAA MOSFETs with impact of silicon film thickness is analyzed by using 3-D ATLAS TCAD device simulator. It is demonstrated that depending on gate voltage, DGAA MOSFET has larger value of drain current (Ids), transconductance (gm) and gain. Results demonstrate that drain current, transconductance, device gain and transconductance to drain current ratio (gm/Ids) improves when temperature is decreased. DGAA MOSFET shows improvement in analog/RF performance, suppressed Short Channel Effects (SCEs) and harmonics distortions due to more gate controllability on the channel charge.

Complex State Variables as Analytical Tool for Control System Design of Medium-Voltage Drives

Complex state variables are used to analyze the dynamics of medium-voltage drives. These operate at low switching frequency to reduce the dynamic losses of the power semiconductor devices. It results in a low sampling rate of the digital signal processing system, causing signal delays that deteriorate the dynamic behavior. Undesired cross-coupling results between the current components id and iq. The effect is shown to be even more adverse than described by the conventional control theory. The solution is modeling the system by single-complex state variables. These permit designing a current controller of high dynamic performance, which exhibits zero cross-coupling. Improved performance at very low switching frequency is demonstrated by experimental results.

Editorial Note: Journal of Physiotherapy and Physical Rehabilitation

Journal of Physiotherapy and Physical Rehabilitation (JPPR) has successfully completed 4 years of successful Journey and is all set for the running year. It provides quarterly publication of articles in all the areas related to Addiction Rehabilitation, Alternative medicine, Cardiac Rehabilitation, Clinical Reflexology, Exercise, Hemipelvectomy, Multiple Sclerosis, Musculoskeletal Pain, and Myofascial Pain including all current researches. We are highly glad to mention that during the year 2019, all issues (4 issues) of Volume 4 were published online within the given time frame and print issues were also brought out and dispatched within 30 days of publishing the issue online. Journal impact factor of 2019 was approximately calculated by dividing the number of articles published in 2017 and 2018 with the number of times they are cited in the Google Scholar citation database. The current NLM ID is 101695557.

Optimization of n-MOS 6T Nanowire SRAM Bit Cell Based on Nanowires Ratio of SiNWTs

In nowadays technology, the primary memory structure widely used in many digital circuit applications is a six transistor (6T) Static Random Access Memory (SRAM) bit cell. The main reason for minimizing memory bit cell to nanodimensions is to provide the SRAM integrated circuits (ICs) with the possible largest memory size per one chip, and the main unit in 6T SRAM bit cell is the MOSFET. One of the new MOSFET structures that overcome conventional MOSFET structure problems under minimization towards nanodimension is the silicon nanowire transistor (SiNWT). This study is the first to explore and optimize the nanowire ratio of driver to load (KD/KL) for a six n-channel SiNWT-based SRAM bit cell. The MuGFET simulation tool has been used to calculate the output characteristics of each transistor individually, and then these characteristics are implemented in the MATLAB software to produce the final static butterfly and current characteristics of nanowire 6T-SRAM bit cell. The demonstration of the driver to load transistors’ nanowires ratio optimizations of nanoscale n-type SiNWT-based SRAM bit cell has been discussed. In this research, the optimization of KD/KL will strongly depend on inflection voltage and high and low noise margins (NMs) of butterfly characteristics. The improvement of NMs of butterfly characteristics has been done by increasing the drain current (Ids) of the driver transistor. Also, the optimization in principle will depend on whether NMs are equal and high, and the inflection voltage (Vinf) is near to Vdd/2 values as possible. These principles have been used as limiting factors for optimization. The results show that the optimization strongly depends on the nanowire ratio, and the best ratio was KD/KL 4. The increase in KD/KL leads to a continuous increase in NMH, acceptable NML and low percentage increment of static power consumption (ΔP %) at KD/KL 4.

Different JFET Designs on Conduction and Short-Circuit Capability for 3.3 kV Planar-Gate Silicon Carbide MOSFETs

Both large current capability and strong short-circuit (SC) ruggedness are necessary for 3.3 kV SiC MOSFETs to improve system efficiency and reduce costs in industrial and traction applications. In this paper, the effects of Junction Field Effect Transistor (JFET) region width and JFET doping (JD) on conduction and SC capability of the 3.3 kV planar-gate SiC MOSFETs are systematically investigated by experiments and simulations. When the JFET width (WJFET) of device without JD is smaller, the positive temperature coefficient of the special on-resistance (Ron,SP) is larger. The JD is effective to improve the Ron,SP, but excessive electric field in gate oxide induced by JD should be paid more attention. The optimization of WJFET can be used to improve both Ron,SP and short circuit withstanding time (SCWT) at the same time. The drain-source current (Ids) and SCWT of the optimized devices are 50 A and more than $20~{\mu }\text{s}$ , respectively, which is state-of-the-art for 3.3 kV SiC MOSFETs.

A Systematic State-of-the-Art Analysis of Multi-Agent Intrusion Detection

Multi-agent architectures have been successful in attaining considerable attention among computer security researchers. This is so, because of their demonstrated capabilities such as autonomy, embedded intelligence, learning and self-growing knowledge-base, high scalability, fault tolerance, and automatic parallelism. These characteristics have made this technology a de facto standard for developing ambient security systems to meet the open and dynamic nature of today’s online communities. Although multi-agent architectures are increasingly studied in the area of computer security, there is still not enough empirical evidence on their performance in intrusions and attacks detection. The aim of this paper is to report the systematic literature review conducted in the context of specific research questions, to investigate multi-agent IDS architectures to highlight the issues that affect their performance in terms of detection accuracy and response time. We used pertinent keywords and terms to search and retrieve the most recent research studies, on multi-agent IDS architectures, from the major research databases and digital libraries such as SCOPUS, Springer, and IEEE Explore. The search processes resulted in a number of studies; among them, there were journal articles, book chapters, conference papers, dissertations, and theses. The obtained studies were assessed and filtered out, and finally, there were over 71 studies chosen to answer the research questions. The results of this study have shown that multi-agent architectures include several advantages that can help in the development of ambient IDS. However, it has been found that there are several issues in the current multi-agent IDS architectures that may degrade the accuracy and response time of intrusions and attacks detection. Based on our findings, the issues of multi-agent IDS architectures include limitations in the techniques, mechanisms, and schemes used for multi-agent IDS adaptation and learning, load balancing, scalability, fault-tolerance, and high communication overhead. It has also been found that new measurement metrics are required for evaluating multi-agent IDS architectures.

Photoconductivity study of spray pyrolized pure and Cu-modified SrTiO3 thin films

The SrTiO3 (STO) and Cu-STO nanostructured thin films were prepared using the spray pyrolysis technique. So prepared films were characterized for structural, electrical and optical and photoconductivity properties. The FE-SEM showed with inhomogeneous grain growth. Scherrer formula used to calculate particle size. The band gap, activation energies are estimated. AFM results were analyzed to estimate roughness. Absorbance and band gaps are calculated. The tungsten 100 W bulb was used to irradiate the films. The nature of I-V characteristics of the films changes with the ranges of applied bias. The effect of electric field and intensity relies photoconductivity of the films. The photo generated current Ip and dark current Id varies according to the power law I α Vm with the applied field and intensity of illumination, due to the defect related mechanism including both recombination centres and traps. The variation in linearity is attributed to flow of trap limited as well as space charge limited current inside the material. Doping of Cu led to the introduction of a high concentration of oxygen vacancies on the surface of the STO lattice. Consequently, to maintain the regional charge balance of STO, Cu2+ could be substituted for Sr2+. Moreover, oxygen vacancies induced localized states into the band gap of the modified STO and acted as photoinduced charge traps, thus promoting the photoconductivity process. The photoconductivity of Cu modified films was found to be more than that of pure STO thin films. This study will have significant impact on the use of Cu-STO in optoelectronics devices.

Investigation of Pd|HfO-=SUB=-2-=/SUB=-|AlGaN|GaN Enhancement-Mode High Electron Mobility Transistor with Sensitization, Activation, and Electroless-Plating Approaches

A new Pd|HfO2|AlGaN|GaN metal-oxide-semiconductor (MOS) enhancement-mode high electron mobility transistor (HEMT) is fabricated with low-temperature sensitization, activation, electroless-plating, and two-step gate-recess approaches. Experimentally, a high positive threshold voltage Vth of 1.96 V, a very low gate leakage IG of 6.3·10-8 mA/mm, a high maximum extrinsic transconductance gm,max of 75.3 mS/mm, a high maximum drain saturation current ID,max of 266.9 mA/mm, and a high ON/OFF current ratio of 7.6·107 are obtained at 300 K. Moreover, the related temperature-dependent characteristics, over temperature ranges from 300 to 500 K, are comprehensively studied. The very low temperature coefficients on gate current, drain saturation current, transconductance, and threshold voltage confirm the thermal-stable capability of the studied device. Therefore, based on these advantages, the studied Pd|HfO2|AlGaN|GaN MOS structure is suitable for the development of high-performance HEMTs. Keywords: HfO2, AlGaN|GaN, metal-oxide-semiconductor, high electron mobility transistor, electroless plating, gate recess, threshold voltage.

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.

Investigation on noise performance of InAsxSb1−x MOSFETs with compositional variations

Using numerical analysis we investigate the thermal and low frequency noise (LFN) performance of InAsxSb1−x-channel nMOSFETs having various As mole fractions x ranging 0.15–0.85 at channel length of 65 nm. The models used in the simulation are calibrated by comparing simulated transfer characteristic curve with experimental characteristic reported elsewhere. The numerically obtained values of drain current ID and transconductance gM are used to compute power spectral density of drain current SID/ID2, noise resistance Rn and minimum noise figure NFmin as a function of As composition fraction x. The minimum noise figure NFmin of 1.35 dB is obtained for thermal noise with x = 0.15 at frequency of 5 GHz and gate bias of 1 V. Our investigation reveals that LFN as well as thermal noise can be suppressed by proper selection of As mole fraction in InAsxSb1−x n-channel MOSFETs.

Chemically Functionalised Graphene FET Biosensor for the Label-free Sensing of Exosomes

A graphene field-effect transistor (gFET) was non-covalently functionalised with 1-pyrenebutyric acid N-hydroxysuccinimide ester and conjugated with anti-CD63 antibodies for the label-free detection of exosomes. Using a microfluidic channel, part of a graphene film was exposed to solution. The change in electrical properties of the exposed graphene created an additional minimum alongside the original Dirac point in the drain-source current (Ids) - back-gate voltage (Vg) curve. When phosphate buffered saline (PBS) was present in the channel, the additional minimum was present at a Vg lower than the original Dirac point and shifted with time when exosomes were introduced into the channel. This shift of the minimum from the PBS reference point reached saturation after 30 minutes and was observed for multiple exosome concentrations. Upon conjugation with an isotype control, sensor response to the highest concentration of exosomes was negligible in comparison to that with anti-CD63 antibody, indicating that the functionalised gFET can specifically detect exosomes at least down to 0.1 μg/mL and is sensitive to concentration. Such a gFET biosensor has not been used before for exosome sensing and could be an effective tool for the liquid-biopsy detection of exosomes as biomarkers for early-stage identification of diseases such as cancer.

Investigation of the aging of power GaN HEMT under operational switching conditions, impact on the power converters efficiency

This paper investigates the aging of a 650 V, 30 A GaN HEMT power transistor under operational switching conditions. The switching stress respects the Safe Operation Area (SOA) of the tested transistor. The aging campaign lasted 1008 h and was carried out through a developed switching application with high power efficiency. The global aging results show the degradation of five parameters: drain current ID, on-state resistance RDS(ON), transconductance gm, gate leakage current IGSS, and threshold voltage VTH. The major causes that affect the reliability of the GaN HEMT are hard switching, long time of test and high intensity of the stress. The existence of trapped charge in the gate-drain access region after aging is demonstrated using pulsed measurements. The effects of this degradation on power converters are studied by modeling the static characteristics of the aged GaN HEMT using an accurate method based on the Levenberg-Marquardt Algorithm. The accuracy and consistent convergence of the developed SPICE model provide a good way to investigate the reliability of GaN HEMTs by a simulation approach.

Radiation-Induced DC Parametric Degradation of Enhancement Mode GaN-on-(111)Silicon High-Electron-Mobility Transistors

AlGaN/GaN high-electron-mobility transistors (HEMTs) for applications in radiation environments has required the exact determination of their radiation hardness. Although bulk GaN is the preferred substrate for the epitaxial growth of GaN and AlGaN, (111) silicon is a possible substrate for HEMT devices. The stability of electrical parameters of enhancement-mode (E-mode) GaN HEMTs under gamma irradiation is an essential characterization for reliability. The present work reports the transfer characteristics degradation of E-mode GaN HEMTs under various total dose irradiation from 5krad up to 60Mrads. This represents the first comprehensive total dose study ranging from a few krads up the tens of Mrads. The measured device-to-device variations within groups of devices are presented. The evolutions of critical DC parameters with accumulated total dose is found to be significant at low doses and saturates at high dose levels. The degradation mechanism is very similar to the reported radiation-induced shallow electron traps that trap and release electrons in the near surface GaN and AlGaN layers. Due to the unique properties including high breakdown voltage, high electron mobility and high thermal stability, wide-bandgap semiconductor power electronic devices, especially Gallium Nitride (GaN) high-electron-mobility transistors (HEMTs), have shown great promise in space, defense and nuclear applications, which often involve radiation-hardened electronics that require high radiation tolerance to fluxes of neutrons or gamma ray of devices. To turn the promising potential of GaN HEMTs into reality, investigations on the influence of irradiation on the device performance and reliability are essential. Many studies have investigated the radiation hardness of group III–nitride compound semiconductor devices under various irradiation types, such as electrons, protons, neutrons, and X-rays and at various total irradiation doses. They generally showed higher radiation tolerance compared with Si because of high displacement energy of GaN, demonstrating the favorability of GaN devices in hard radiation environments. Many studies have investigated the influence of 60Co gamma radiation on the device electrical characteristics. However, they were all focusing on depletion mode (D-mode) devices. Enhancement mode (E-mode) GaN-on-Si transistors have been commercially available for years. Their major advantages over D-mode devices are elimination of negative voltage supply and the enabling of direct-coupled FET logic (DCFL) for digital circuits. They also improve the efficiency of commercial DC-DC converters in various power levels and topologies. A previous work on gamma radiation of E-mode GaN-on-Si HEMTs only reported cumulative total doses of up to 1 Mrads (Si). The present work provides a complete coverage of low-to-high irradiation doses from 5krads up to 60Mrads (Si), for commercially available E-mode GaN HEMTs and the devices are characterized to gauge variations in the critical DC parameters. To the best of the author’s knowledge, the present work is the first to investigate the gamma radiation tolerance of E-mode GaN HEMTs covering such a wide range of total doses. This facilitates the observation of the complete degradation behavior of DC parameters in hard radiation applications of the E-mode GaN HEMTs. The devices were supplied in the form of 0.9mm square passivated die with round solder bumps for contacts. They have a rated continuous drain-to-source voltage VDS of 60V, and a rated continuous drain current ID of 1A. These GaN-on-Si devices were fabricated on Si wafers considering process compatibility and cost. An aluminum nitride (AlN) thin layer was grown on the Si wafer to be a seed layer for the AlGaN/GaN heterostructure. Subsequently, the AlGaN/GaN heterostructure was grown on the AlN layer, with a thin AlGaN layer grown above the highly resistive GaN serving as a strained interface between the GaN and AlGaN crystal layers, allowing the creation of a two-dimensional electron gas (2DEG) filled with abundant free electrons with ultra-high mobility. The gate electrode was processed subsequently forming a depletion region under the gate. As an E-mode transistor, the device is turned on by applying a positive bias to the gate. All the irradiations were conducted at room temperature by 60Co gamma-rays with a flux of 318.5Rads (Si)/s, at the dry-cell panoramic gamma irradiator in the University of Maryland Radiation Facilities. The entire irradiation procedure consists of two parts. The first part is higher-dose irradiation with total doses of up to 60Mrads based on two stages. At the first stage, the devices were irradiated at 10Mrads, while at the second stage, the devices were irradiated for another 50Mrads, with three of them taken out after 25Mrads during the second stage. The second part is lower-dose irradiations with total doses of up to 2Mrads. The temperature throughout the irradiation process was monitored to be below 30°C.