Date of Award

Summer 8-16-2024

Level of Access Assigned by Author

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Electrical and Computer Engineering

Advisor

Mauricio Pereira da Cunha

Second Committee Member

Nuri Emanetoglu

Third Committee Member

Nicholas Bingham

Abstract

Oscillator circuits are at the heart of electronics required for communication, frequency control, and sensing. Crystal oscillators, in particular, present very attractive characteristics, such as their low power consumption and high frequency stability. These circuits employ acoustic waves devices as the frequency control element, often a bulk acoustic wave (BAW) resonator. There is an increasing need for communication and sensing circuitry capable of withstanding high temperatures (HT) and harsh environments (HE) in many industries, and a crystal oscillator capable of insertion in such environments and of continuous operation from room temperature to HT is a beneficial addition to many HT and HE systems. One central challenge to implementing these circuits at HT is the temperature limitation of traditional silicon semiconductor devices. Alternative semiconductor technologies such as SiC and GaN are able to operate above the temperature limits of silicon and have been well studied in the literature. Such devices are commercially available but are often temperature limited by their packaging. As part of this research, a commercially available bare-die GaN high electron mobility transistor (HEMT) was characterized between room temperature and 500°C. The characterization data was used to improve the high temperature performance of the SPICE model provided by the vendor and used to design the oscillator circuit. Another important component in the design of such HT crystal oscillators is the temperature dependence of BAW crystal resonator’s characteristics over wide temperature ranges. It is necessary to understand the temperature behavior of the crystal’s parameters in order to design a crystal oscillator circuit capable of operation over a wide temperature range. Hence, a commercially available quartz crystal microbalance (QCM) BAW device was characterized from room temperature to 400°C. The equivalent circuit parameters of the modified Butterworth-Van Dyke model around the resonant frequency were extracted for temperatures up to 400°C and used in the oscillator circuit design. A quartz crystal oscillator utilizing a commercially available AlGaN /GaN HEMT and a commercial BAW QCM was designed, simulated, fabricated, and demonstrated from room temperature up to 400°C in this research. Six oscillator topologies were compared in analysis and simulation for their ability to sustain continuous oscillation over the widest temperature range. The most promising topology was identified and implemented on a high temperature platform consisting of an alumina substrate circuit board, crystal mounting structure, and in-house fabricated passive components. The oscillator was demonstrated to operate continuously over the entire temperature range from room temperature to 400°C with an overall frequency variation of less than 1%. The oscillation frequency recovered to within 0.01% of its original room temperature value, and the signal amplitude recovered to within 3% of its original room temperature value. The frequency behavior and recoverability of the circuit make it an excellent candidate for high temperature and harsh environment sensing, frequency control, and communication systems.

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