The fact that wide bandgap semiconductors are capable of electronic functionality at much higher temperatures than silicon has partially fueled their development, particularly in the case of SiC. It appears unlikely that wide bandgap semiconductor devices will find much use in low-power transistor applications until the ambient temperature exceeds approximately 300/spl deg/C, as commercially available silicon and silicon-on-insulator technologies are already satisfying requirements for digital and analog VLSI in this temperature range. However practical operation of silicon power devices at ambient temperatures above 200/spl deg/C appears problematic, as self-heating at higher power levels results in high internal junction temperatures and leakages. Thus, most electronic subsystems that simultaneously require high-temperature and high-power operation will necessarily be realized using wide bandgap devices, once they become widely available. Technological challenges impeding the realization of beneficial wide bandgap high ambient temperature electronics, including material growth, contacts, and packaging, are briefly discussed.

High-temperature electronics - a role for wide bandgap semiconductors?

Journal of Applied physics,Vol.33 : 1962年に発表されたレオロジー関連の論文

Gallium oxide (Ga2O3) is emerging as a viable candidate for certain classes of power electronics with capabilities beyond existing technologies due to its large bandgap, controllable doping, and the availability of large diameter, relatively inexpensive substrates. These applications include power conditioning systems, including pulsed power for avionics and electric ships, solid-state drivers for heavy electric motors, and advanced power management and control electronics. Wide bandgap (WBG) power devices offer potential savings in both energy and cost. However, converters powered by WBG devices require innovation at all levels, entailing changes to system design, circuit architecture, qualification metrics, and even market models. The performance of high voltage rectifiers and enhancement-mode metal-oxide field effect transistors benefits from the larger critical electric field of β-Ga2O3 relative to either SiC or GaN. Reverse breakdown voltages of over 2 kV for β-Ga2O3 have been reported, either with or without edge termination and over 3 kV for a lateral field-plated Ga2O3 Schottky diode on sapphire. The metal-oxide-semiconductor field-effect transistors fabricated on Ga2O3 to date have predominantly been depletion (d-mode) devices, with a few demonstrations of enhancement (e-mode) operation. While these results are promising, what are the limitations of this technology and what needs to occur for it to play a role alongside the more mature SiC and GaN power device technologies? The low thermal conductivity might be mitigated by transferring devices to another substrate or thinning down the substrate and using a heatsink as well as top-side heat extraction. We give a perspective on the materials’ properties and physics of transport, thermal conduction, doping capabilities, and device design that summarizes the current limitations and future areas of development. A key requirement is continued interest from military electronics development agencies. The history of the power electronics device field has shown that new technologies appear roughly every 10-12 years, with a cycle of performance evolution and optimization. The older technologies, however, survive long into the marketplace, for various reasons. Ga2O3 may supplement SiC and GaN, but is not expected to replace them.

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Perspective: Ga2O3 for ultra-high power rectifiers and MOSFETS

Silicon carbide (SiC) is one of the most promising materials for applications in harsh environments thanks to its excellent electrical, mechanical, and chemical properties. The piezoresistive effect of SiC has recently attracted a great deal of interest for sensing devices in hostile conditions. This paper reviews the piezoresistive effect of SiC for mechanical sensors used at elevated temperatures. We present experimental results of the gauge factors obtained for various poly-types of SiC films and SiC nanowires, the related theoretical analysis, and an overview on the development of SiC piezoresistive transducers. The review also discusses the current issues and the potential applications of the piezoresistive effect in SiC. [2015-0092]

/pdf/the-piezoresistive-effect-of-sic-for-mems-sensors-at-high-5nj84nysyq.pdf

The Piezoresistive Effect of SiC for MEMS Sensors at High Temperatures: A Review

Advances in silicon carbide microfabrication and growth process optimization for silicon carbide nanostructures are ushering in new opportunities for microdevices capable of operation in a variety of demanding applications, involving high temperature, radiation, or corrosive environment. This review focuses on the materials science and processing technologies for silicon carbide thin films and low dimensional structures, and details recent progress in manufacturing technology, including deposition, metallization, and fabrication of semiconductor microdevices, with emphasis on sensor technology. The challenges remaining in developing silicon carbide as a mainstay materials platform are discussed throughout.

Advances in silicon carbide science and technology at the micro- and nanoscales

Uncooled MEMS-based 4H-SiC Wheatstone bridge configured piezoresistive pressure sensors were demonstrated from 23 °C to 800 °C. The full-scale output (FSO) voltage exhibited gradual decrease with increasing temperature from 23 °C to 400 °C, then swung upward as temperature increased further to where the values measured at 800 °C were nearly equal to or higher than the room temperature values. This newly observed FSO behavior in 4H-SiC contrasts sharply with the FSO behavior of silicon piezoresistive sensors that decrease continuously with increasing temperature. The increase in the sensor output sensitivity at 800 °C implies higher signal to noise ratio and improved fidelity, thereby offering promise of further insertion into >600 °C environments without the need for cooling and complex signal conditioning.

4H-SiC Piezoresistive Pressure Sensors at 800 °C With Observed Sensitivity Recovery

We report the result of the development and analysis of Ti/TaSi2/Pt high temperature ohmic contact metallizations on n-type 4H– and 6H–SiC that can successfully withstand 1000 h of 600 °C thermal treatment in air. Understanding the reaction kinetics and dominant failure mechanisms enabled metal thicknesses in the multilayer stack to be optimized, thereby providing stable specific contact resistivity in the range of 1–6×10−5 Ω cm2 on the n-type 4H–SiC and 6H–SiC epilayers throughout the duration of heat treatment in air. The deleterious effects of platinum in a platinum-rich silicide and the benefits in a platinum Si-rich silicide were identified within the multilayer system. A high temperature ohmic contact figure of merit is proposed as a reliability benchmark and calculated for the contacts to 4H– and 6H–SiC.

Reliability assessment of Ti/TaSi2/Pt ohmic contacts on SiC after 1000 h at 600 °C

This letter reports fabrication and testing of integrated circuits (ICs) with two levels of interconnect that consistently achieve greater than 1000 h of stable electrical operation at 500 °C in air ambient. These ICs are based on 4H-SiC junction field-effect transistor technology that integrates hafnium ohmic contacts with TaSi2 interconnects and SiO2 and Si3N4 dielectric layers over $\sim 1$ - $\mu \text{m}$ scale vertical topology. Following initial burn-in, important circuit parameters remain stable within 15% for more than 1000 h of 500 °C operational testing. These results advance the technology foundation for realizing long-term durable 500 °C ICs with increased functional capability for sensing and control combustion engine, planetary, deep-well drilling, and other harsh-environment applications.

Prolonged 500 °C Demonstration of 4H-SiC JFET ICs With Two-Level Interconnect

Silicon carbide (SiC) based gas sensors have the ability to meet the needs of a range of aerospace applications including leak detection, environmental control, emission monitoring, and fire detection. While each of these applications require that the sensor and associated packaging be tailored for that individual application, they all require sensitive detection. The sensing approach taken to meet these needs is the use of SiC as a semiconductor in a Schottky diode configuration due to the demonstrated high sensitivity of Schottky diode-based sensors. However, Schottky diode structures require good control of the interface between the gas sensitive metal and SiC in order to meet required levels of sensitivity and stability. Two examples of effort to better control the SiC gas sensitive Schottky diode interface will be discussed. First, the use of chrome carbide as a barrier layer between the metal and SiC is discussed. Second, we report the first use of atomically flat SiC to provide an improved SiC semiconductor surface for gas sensor deposition. An example of the demonstration of a SiC gas sensor in an aerospace applications is given. It is concluded that, while significant progress has been made, the development of SiC gas sensor systems is still at a relatively early level of maturity for a number of applications.

Development of SiC-based Gas Sensors for Aerospace Applications

Prolonged Venus surface missions (lasting months instead of hours) have proven infeasible to date in the absence of a complete suite of electronics able to function for such durations without protection from the planet’s extreme conditions of ~460°C, ~9.3 MPa (~92 Earth atmospheres) chemically reactive environment. Here, we report testing data from a successful two-month (60-day) operational demonstration of two 175-transistor 4H-SiC junction field effect transistor (JFET) semiconductor integrated circuits directly exposed (no cooling and no protective chip packaging) to a high-fidelity physical and chemical reproduction of Venus surface atmospheric conditions in a test chamber. These results extend the longest reported duration of electronics operation in Venus surface atmospheric conditions almost threefold and were accomplished using prototype SiC JFET chips of more than sevenfold increased complexity. The demonstrated advancement marks a significant step toward realization of electronics with sufficient complexity and durability for implementing robotic landers capable of returning months of scientific data from the surface of Venus.

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Dorothy Lukco

Papers

4H-SiC Piezoresistive Pressure Sensors at 800 °C With Observed Sensitivity Recovery

Reliability assessment of Ti/TaSi2/Pt ohmic contacts on SiC after 1000 h at 600 °C

Prolonged 500 °C Demonstration of 4H-SiC JFET ICs With Two-Level Interconnect

Development of SiC-based Gas Sensors for Aerospace Applications

Operational Testing of 4H-SiC JFET ICs for 60 Days Directly Exposed to Venus Surface Atmospheric Conditions