Zachary D. Schwartz

High-temperature RF probe station for device characterization through 500/spl deg/C and 50 GHz

A high-temperature measurement system capable of performing on-wafer microwave testing of semiconductor devices has been developed. This high-temperature probe station can characterize active and passive devices and circuits at temperatures ranging from room temperature to above 500/spl deg/C. The heating system uses a ceramic heater mounted on an insulating block of NASA Shuttle tile. The temperature is adjusted by a graphical computer interface and is controlled by the software-based feedback loop. The system is used with a vector network analyzer to measure scattering parameters over a frequency range from 1 to 50 GHz. The microwave probes, cables, and inspection microscope are all shielded to protect from heat damage. The high-temperature probe station has been successfully used to characterize gold transmission lines on silicon carbide at temperatures up to 540/spl deg/C.

1-GHz, 200/spl deg/C, SiC MESFET Clapp oscillator

A SiC Clapp oscillator fabricated on an alumina substrate with chip capacitors and spiral inductors is designed for high-temperature operation at 1GHz. The oscillator operated from 30/spl deg/C to 200/spl deg/C with an output power of 21.8dBm at 1GHz and 200/spl deg/C. The efficiency at 200/spl deg/ C is 15%. The frequency variation over the temperature range is less than 0.5%.

High temperature performance of a SiC MESFET based oscillator

A hybrid, UHF-Band differential oscillator based on 10 W SiC RF Power Metal Semiconductor Field Effect Transistor (MESFET) has been designed, fabricated and characterized through 475 °C. The circuit is fabricated on an alumina substrate with thin film spiral inductors, chip capacitors, chip resistors, and wire bonds for all crossovers and interconnects. The oscillator delivers 15.7 dBm at 515 MHz into a 50 Ω load at 125 °C with a DC to RF conversion efficiency of 2.8 %. After tuning the load impedance, the oscillator delivers 18.8 dBm at 610 MHz at 200 °C with a DC to RF conversion efficiency of 5.8 %. Finally, by tuning the load and bias conditions, the oscillator delivers 4.9 dBm at 453 MHz at 475 °C. Index Terms — oscillators, wide-bandgap, SiC, High Temperature.

Measured propagation characteristics of coplanar waveguide on semi-insulating 4H-SiC through 800 K

Wireless sensors for high temperature industrial applications and jet engines require RF transmission lines and RF integrated circuits (RFICs) on wide bandgap semiconductors such as SiC. In this paper, the complex propagation constant of coplanar waveguide fabricated on semi-insulating 4H-SiC has been measured through 813 K. It is shown that the attenuation increases 3.4 dB/cm at 50 GHz as the SiC temperature is increased from 300 K to 813 K. Above 500 K, the major contribution to loss is the decrease in SiC resistivity. The effective permittivity of the same line increases by approximately 5% at microwave frequencies and 20% at 1 GHz.