Design, Fabrication, and Characterization of High-Current Optically-Triggered Power Transistors

The main focus of this thesis is the design, simulation, optimization, fabrication and characterization of a high-current and low on-state voltage optically-triggered power transistor (OTPT). The major power application investigated for this designed OTPT in this thesis is for single-bias all-optical ETO thyristor. Electrical ETO thyristors have been already developed to facilitate more reliable options for high-power thyristors in pulsed-power applications. Electrical ETOs have been shown to achieve better turn-on and turn-off controllability, using two MOSFET transistors to assist the switching transition of the main high-power thyristor. Furthermore, ETOs benefit from a turn-off snubberless solution and mitigate the high di/dt and dv/dt problems associated with gate turn-off (GTO) thyristors and MOS turn-off (MTO) thyristors. However, all the above-mentioned electrically-triggered high-power thyristors including the electrical ETOs may be susceptible to electromagnetic interference (EMI). As such, optical ETO thyristors have been then introduced to overcome the EMI effect and deliver a single-biased technology for high-power thyristors. Optical links are immune to EMI noise and bring more flexibility for conductivity modulation by changing the optical intensity. In several applications, the OTPT is operated as the optical driver in which high-current and high-voltage stress is not an issue since the OTPT bias is separate from the main power stage bias. However, for an optical ETO thyristor, the OTPT is placed in series with the main power device (i.e., the SiC thyristor). Consequently, the rated current of the OTPT is the same as that for the SiC thyristor. Therefore, special designs and fabrication techniques are required to yield the high-current capability for the OTPT. Since almost all the bias voltage and the leakage current are supposed to be blocked by the high-power SiC thyristor in the optical ETO application, one can benefit from designing a somewhat leaky device for realizing the OTPT while focusing on other important performance parameters such as higher rated current, lower on-state voltage, and smaller rise time. Therefore, the main goal and motivation of this thesis are to increase the power and current rating of the designed OTPT while keeping the on-state voltage and switching delay times in an acceptable range. Further, the conductivity-modulation capability of the OTPT is studied to be utilized in series-connected optical ETO thyristors. This way, one can achieve an active optical driver for series connection of high-power thyristors without the need of using turn-off dv/dt snubber circuits and heavy capacitors for voltage balance.