The Effect of the Doping Concentration in the Anode Region on the Voltage Temperature Coefficient of the FRD Chips

Fast Recovery Diode chips are widely used in power systems, often employed in reverse parallel packages with Insulated Gate Bipolar Transistor chips. Due to the growing demand for increased power system equipment capacity, there has been a corresponding rise in the requirement for the amount of FRD chips in IGBT devices. Consequently, the issue of parallel current evenness of FRD chips has garnered greater attention. Traditional FRD chips exhibit a negative voltage temperature coefficient, which can result in “current-heat” negative feedback due to uneven current distribution when operated in parallel and may lead to chip failure under severe conditions. To address this problem, a method is presented in this paper to optimize the forward voltage temperature coefficient of FRD chips by analyzing carrier concentration distribution and mobility distribution within the drift region through establishing FRD chip simulation models. This method involves reducing the anode doping concentration as a means of regulating the voltage temperature coefficient of FRD chips. Based on this approach, the 3300V 1125A FRD chips are fabricated and tested. It demonstrates less than 15% deviation between measured results and simulated results for room temperature forward voltage, high temperature forward voltage and voltage temperature coefficient, thereby validating the effectiveness of the proposed method.

I. Introduction

With the rapid development of China's power industry, numerous high-capacity and long-distance ultra-high voltage direct current (UHVDC) transmission proj ects have been successfully implemented [1]–[4]. In line with the national “Belt and Road” development strategy and the “double-carbon” goal, there is a pressing demand for large capacity power transmission. Consequently, an increasing number of insulated gate bipolar transistors (IGBTs) and fast recovery diode (FRD) power chips are being employed in parallel applications. The problem of current equalization between chips is gradually valued. ABB has reported that when two IGBT modules are used in parallel, the maximum deviation rate of current reaches 4.5% [5]. SEMIKRON has also reported that, under a 1500A operating condition with 20 modules, there is a maximum inter-module current value of 103A and a minimum value of 73. 5A[6]. This uneven distribution poses risks such as chip overpower burnout leading to module failure during operation. Our own chip testing process has revealed similar issues caused by uneven inter-chip currents. Both ABB and SEMIKRON emphasize that FRD chips with positive voltage temperature coefficients are more suitable for large-scale parallel applications [5], [6].