Papers by Keyword: High Temperature Electronics

Abstract: This study presents electrical transport properties of a catalyst-free grown single aluminum nitride nanowire field effect transistor (AlNNW-FET) exhibiting a very high transconductance of 26.9 pS, high on/off current ratio of 795.9, high conductivity of 9.8 x 10^-4 Ω^-1.cm^-1, and a very low leakage current of 10 pA. The conductivity of AlN nanowire is two orders of magnitude higher than the reported studies. The AlNNW-FET reveals a dominant p-type conductivity. The p-type conductivity can be attributed to aluminum vacancies and complexes composed of Al vacancies and oxygen impurities. In consequence, the fabricated AlNNW-FET with high-performance, cost-effectiveness, and high-power efficiency is very well suited for use in low power and high temperature nanoelectronic and piezoelectric sensor applications, as well as integrated electro-optical devices including optomechanical devices and pyroelectric photodetectors.

Abstract: This report describes the first to fabricate GaN p-n junction diodes on free-standing GaN substrates with a 3mm diameter. For the diode of 3 mm in diameter, the specific on-resistance and the breakdown voltage were 124 mΩ•cm2 (at 4.0 V) and -450 V, respectively. Consequently, combination of our material and device processing revealed a record fabricated device size with a high breakdown voltage and low forward leakage current in GaN vertical diodes.

Abstract: – 4H-SiC MESFET transistors are very attractive devices for high temperature application and communications. The JFET and MESFET transistors have a promising potential for integrated circuits able to operate at high temperature and harsh radiation environments, due to the superior electrical, mechanical and chemical proprieties of 4H-SiC. Progresses in the manufacturing of high quality SiC substrates open the possibility to new circuit applications.

Abstract: The solder joints of surface mount components (SMCs) experience thermal degradation culminating in creep and plastic shear strain deformation when subjected to cyclic temperature load over time. Degradation at the joints is due to thermal stress induced by the incompatible, differential and nonlinear expansion mismatch of the different bonded materials in the assembly. The stress magnitude influences the strain behaviour. Plastic strain response of solder joint is critical at the materials interface at the lower part of the joint due to the occurrence of wider variation in the coefficient of thermal expansion of the bonded materials and this may lead to static structural failure. The life expectancy of electronic components reduces exponentially as the operating temperature increases thus making reliability a key concern for electronic systems operating at high temperatures and in harsh environments. This paper reports on the numerical investigation of thermo-mechanical response of a critical BGA joint especially the character of plastic deformation of SnPb solder used in forming the joint as well as the joint’s high temperature reliability. The analysis uses a 3-D models to predict the effect of the transient thermal load on the static structural integrity of a single BGA joint. In this study, the base diameter of solder ball (interface between the PCB, copper pad and the solder) experienced higher damage than the top diameter interconnects. The paper provides a simplified methodology to study the reliability of BGA solder joint at high temperatures excursion.

Abstract: The suitability of normally-off 4H-SiC MOSFETs for high temperature operation in logic gates is investigated. Fowler-Nordheim analysis shows a lowering of the effective tunneling barrier height at elevated temperatures. Trap assisted tunneling induced by carbon interstitials is proposed as the responsible mechanism. Nevertheless, reliability of MOS devices even at 400°C is excellent with an extrapolated critical field of 2.69MV/cm for a 10 year time to dielectric breakdown. The switching behavior of logic gates is also characterized between 25°C and 400°C. Using these logic gates, a fully integrated edge triggered flip-flop is build and high temperature operation is demonstrated.

Abstract: This paper reports fabrication and electrical characterization of 6H-SiC n-channel, depletion-mode, junction-field-effect transistors (JFETs) for use in high-temperature analog integrated circuits for sensing and control in propulsion, power systems, and geothermal exploration. Electrical characteristics of the resulting JFET devices have been measured across the wafer as a function of temperature, from room temperature to 450oC. The results indicate that the JFETs are suitable for high-gain amplifiers in high-temperature sensor signal processing circuits.

Abstract: This paper presents silicon carbide sensor interface circuits and techniques for MEMSbased sensors operating in harsh environments. More specifically, differential amplifiers were constructed using integrated, depletion-mode, n-channel, 6H-SiC JFETs and off-chip passive components. A three-stage voltage amplifier has a differential voltage gain of ~50 dB and a gainbandwidth of ~200 kHz at 450oC, as limited by test parasitics. Such an amplifier could be used to amplify the signals produced by a piezoresistive Wheatstone bridge sensor, for example. Design considerations for 6H-SiC JFET transimpedance amplifiers appropriate for capacitance sensing and for frequency readout from a micromechanical resonator are also presented.

Abstract: Trenched and implanted vertical JFETs (TI-VJFETs) with blocking voltages of 700 V were fabricated on commercial 4H-SiC epitaxial wafers. Vertical p+-n junctions were formed by aluminium implantation in sidewalls of strip-like mesa structures. Normally-on 4H-SiC TI-VJFETs had specific on-state resistance (RO-S ) of 8 mW×cm2 measured at room temperature. These devices operated reversibly at a current density of 100 A/cm2 whilst placed on a hot stage at temperature of 500 °C and without any protective atmosphere. The change of RO-S with temperature rising from 20 to 500 °C followed a power law (~ T 2.4) which is close to the temperature dependence of electron mobility in 4H-SiC.