A monolithic CMOS microhotplate-based conductance-type gas sensor system is described. A bulk micromachining technique is used to create suspended microhotplate structures that serve as sensing film platforms. The thermal properties of the microhotplates include a 1-ms thermal time constant and a 10 C mW thermal efficiency. The polysilicon used for the microhotplate heater exhibits a temperature coefficient of resistance of 1.067 10 3 C. Tin(IV) oxide and titanium(IV) oxide (SnO 2 TiO 2) sensing films are grown over postpatterned gold sensing electrodes on the microhotplate using low-pressure chemical vapor deposition (LPCVD). An array of microhotplate gas sensors with different sensing film properties is fabricated by using a different temperature for each microhotplate during the LPCVD film growth process. Interface circuits are designed and implemented monolithically with the array of microhotplate gas sensors. Bipolar transistors are found to be a good choice for the heater drivers, and MOSFET switches are suitable for addressing the sensing films. An on-chip operational amplifier improves the signal-to-noise ratio and produces a robust output signal. Isothermal responses demonstrate the ability of the sensors to detect different gas molecules over a wide range of concentrations including detection below 100 nanomoles/mole. I. INTRODUCTION C HEMICAL microsensors represent one important application for microelectromechanical systems (MEMS) technology. Microhotplate devices belong to the MEMS family and can be fabricated in commercial CMOS technology using micromachining techniques [1]. Thermally isolated microhotplate structures can be utilized for conductance-type gas sensing [2] or as microscopic infrared sources [3]. The CMOS compatible process realizes a class of devices that are based on thermo-electromechanical effects and are compatible with existing very-large-scale-integration (VLSI) circuit design techniques [4]-[6]. In this paper, a monolithic integration of a gas sensor system based on CMOS-compatible microhotplate technology is presented. There are numerous applications avail-Manuscript

The electrical performance of silicon carbide (SiC) power diodes is evaluated and compared to that of commercially available silicon (Si) diodes in the voltage range from 600 V through 5000 V. The comparisons include the on-state characteristics, the reverse recovery characteristics, and power converter efficiency and electromagnetic interference (EMI). It is shown that a newly developed 1500-V SiC merged PiN Schottky (MPS) diode has significant performance advantages over Si diodes optimized for various voltages in the range of 600 V through 1500 V. It is also shown that a newly developed 5000 V SiC PiN diode has significant performance advantages over Si diodes optimized for various voltages in the range of 2000 V through 5000 V. In a test case power converter, replacing the best 600 V Si diodes available with the 1500 V SiC MPS diode results in an increase of power supply efficiency from 82% to 88% for switching at 186 kHz, and a reduction in EMI emissions.

No abstract

No abstract

This paper reports the design, fabrication and high temperature characteristics of 1 mm 2 , 4 mm 2 and 9 mm 2 4H-SiC p-in rectifiers with 6 kV, 5 kV, and 10 kV blocking voltage, respectively. These results were obtained from two lots in an effort to increase the total power levels on such rectifiers. An innovative design utilizing a highly doped p-type epitaxial Anode layer and junction termination extension (JTE) were used in order to realize good on-state as well as stable blocking characteristics. For the 1 mm 2 and 4 mm 2 rectifier, a forward voltage drop of less than 5 V was observed at 500 A/cm 2 and the peak reverse recovery current shows a modest 50% increase in the 25 C to 225 C temperature range. On the 10 kV, 9 mm 2 rectifier, a forward voltage drop of less than 4.8 V was observed at 100 A/cm 2 in the entire 25 C to 200 C temperature range. For this device, the reverse recovery characteristics show a modest 110% increase in the peak reverse recovery current from 25 C to 200 C. A dramatically low rr of 3.8 C was obtained at a forward current density of 220 A/cm 2 at 200 C for this ultra high voltage rectifier. These devices show that more than three orders of magnitude reduction in reverse recovery charge is obtained in 4H-SiC rectifiers as compared to comparable Si rectifiers.