Micromachined broadband thermocouple microwave power sensors in CMOS technology

This dissertation reports on the design, fabrication, and characterization of broadband thermocouple-based microwave power sensors implemented in standard CMOS technology followed by silicon micromachining. These thermal converters detect true rms value of unknown microwave signals by converting the signals to heat in terminating resistors, and measuring the resulting temperature increase with thermocouples.;The devices are based on coplanar waveguide (CPW) transmission lines fabricated with CMOS aluminum, matching termination resistors of CMOS polysilicon, and aluminum-polysilicon thermocouples. This transmission line based design with matching termination is responsible for extending the operating frequency well into millimeter wave range. The result is a first CMOS compatible sensor with gigahertz operation, which significantly extends previous achievements of thermoconverters that operate up to several hundred megahertz.;Low cost maskless post-process was developed to allow for the removal of silicon substrate in selected areas of the chip. This ultrasonically enhanced hybrid etch is a two-step post-process of isotropic etching using xenon difluoride, followed by ultrasonically enhanced anisotropic etching using ethylenedyamine pyrocatechol in water.;Test sets of CPWs were fabricated through a number of standard CMOS processes and characterized over the frequency range from 0.1 GHz to 50 GHz. It was shown through accurate measurements and new quasi-static model that the highly lossy nature of propagation is due to both transverse and longitudinal currents induced in the silicon substrate. A similar model is given for the improved fully-suspended CPWs to allow fully analytical design for desired characteristic impedance, and predicting performance. The fully-suspended CPWs achieve attenuation below 4 dB/cm at 40GHz. A low measured effective permittivity of ∼1.8 is very uniform over all frequencies of interest.;Two types of micromachined power sensor design were fabricated and characterized using electromagnetic and thermal models and measurements. Both types of sensors operate efficiently to 50 GHz, with maximum sensitivity of 3.04 V/W for Sensor 1, which slowly decreases with frequency to arrive at 2.22 V/W at 50 GHz. Thermal time constant of both devices is ∼1.5 ms. Throughout the 50 GHz frequency range the devices' input reflection is below -10 dB. Below 35 GHz, it is below -20 dB.