Silicon-based insulated gate bipolar transistors (IGBTs) are often regarded as the "CPU" of electrical systems due to their ease of control, high voltage, and high current capabilities. The IGBT is a unidirectional device and needs to be co-packaged with an anti-parallel diode for current freewheeling in inductive loads. They are widely used in power conversion and motor drive hard-switching applications because of their high current density and cost-effectiveness. Reverse conducting IGBTs (RC-IGBTs) incorporate both the IGBT and antiparallel diode into a single chip, offering low cost, compact size, high reliability, and low thermal resistance. However, the application of RC-IGBTs in hard-switching is limited due to the conflicting requirements in carrier distribution between the IGBT...[ Read more ]

Silicon-based insulated gate bipolar transistors (IGBTs) are often regarded as the "CPU" of electrical systems due to their ease of control, high voltage, and high current capabilities. The IGBT is a unidirectional device and needs to be co-packaged with an anti-parallel diode for current freewheeling in inductive loads. They are widely used in power conversion and motor drive hard-switching applications because of their high current density and cost-effectiveness. Reverse conducting IGBTs (RC-IGBTs) incorporate both the IGBT and antiparallel diode into a single chip, offering low cost, compact size, high reliability, and low thermal resistance. However, the application of RC-IGBTs in hard-switching is limited due to the conflicting requirements in carrier distribution between the IGBT and diode modes of operations. To improve the reverse recovery characteristics of RC-IGBTs in the diode mode, it is crucial to lower the reverse recovery loss (E_rec) to reduce switching power loss, decrease the reverse recovery time (T_rr) to support higher switching frequencies, improve the softness factor (S) for effective electromagnetic interference control, and reduce the peak reverse recovery current (I_rrm) to enhance device reliability. This thesis presents the design and characterization of a novel RC-IGBT with superior reverse recovery characteristics for hard-switching applications such as motor drive inverters.

First, the novel RC-IGBT incorporates critical structures such as a punch-through (PT) NPN and a JFET for electron extraction (EE). These structures were designed and experimentally validated by fabricating a discrete PT-NPN diode. Compared with a conventional Self-adjusting P Emitter Efficiency Diode (SPEED), the proposed PT-NPN diode provides a much larger S (+23%), a shorter T_rr (-5%), and a much reduced reverse recovery charge Q_rr (-20%) at a nominal current. Second, the analysis and characterization of the PT-NPN diode are further performed. Numerical analysis shows that the PT voltage V_PT and the P⁺ width ratio are critical parameters to control the hole injection efficiency of the PT-NPN diode. Experimental results show that the leakage current of the PT-NPN diode at 400 K can be kept at a level similar to that of the conventional SPEED with a well-designed V_PT. Compared with SPEED, the PT-NPN diode achieves a reduced I_rrm (-21%) and minimized E_rec (-18%) at a nominal current. It can realize a significantly reduced I_rrm (-42%) even at a small current and a bus voltage of 800 V. Moreover, the better reverse recovery performances of the PT-NPN diode can be maintained at 450 K. Third, the electron extraction mechanism of the PT-NPN diode is fully investigated. Similar to the N-type Schottky barrier, the PT-NPN region in the PT-NPN diode features a unipolar structure for electron unidirectional conduction. Experimental results show that S of the PT-NPN diode is increased by 20% compared with that of a N-Schottky implemented PT-NPN (N-Schottky PT-NPN) diode. In addition, the PT-NPN diode attains a stable BV of 1268 V with a low leakage current; however, the leakage current of the N-Schottky PT-NPN diode is increased by 10 times when the barrier height is varied by 0.3 eV. Finally, the fabrication compatibility of the PT-NPN and JFET structures with conventional RC-IGBT is evaluated, and a new EE RC-IGBT is proposed to enhance the reverse recovery characteristics in the diode mode for hard-switching applications. During the IGBT mode of operation, the EE RC-IGBT demonstrates similar threshold voltage and short circuit capability compared to those of the conventional Floating P-body (FP) RC-IGBT. For reverse conduction in the diode mode, the hole carriers of the EE RC-IGBT are reduced by 66% compared to that of the FP RC-IGBT due to the electron extraction effect. As a result, compared to the fabricated conventional device, the proposed device exhibits a reduction of 20% in I_rrm and 16% in E_rec at a small current. Furthermore, the proposed device shows a 19% increase in S, a 12% reduction in I_rrm, a 14% decrease in Q_rr, and a 10% reduction in E_rec at a nominal current. Experimental results also indicate that the electron extraction does not increase V_F of the proposed device, and the FP and EE RC-IGBTs in the diode mode have the same avalanche capability of absorbing an avalanche energy of 3.37 mJ.