ASEPS: Simulation of the Breakdown Behavior of Power Transistors

Introduction

An exact solution of the Maxwell equations is computationally expensive. However, if we are only interested in analyzing the behavior of the diodes under reverse bias condition, the Maxwell equations can be simplified, whereby an accurate solution can be obtained about 100 times faster.

These simplifications were realized in ASEPS, so that also larger device structures, e.g. multiple transistors with a common substrate, can be simulated efficiently.

When power transistors are exposed to total dose ionizing radiation, e.g. during long space missions or under the influence of the electromagnetic pulse (EMP) after exploding an atomic bomb in the atmosphere, they are being destroyed, as electromagnetic fields can locally be built up that the device is unable to withstand. To counter this problem, it is necessary to harden the transistors against the effects of total dose ionizing radiation by embedding them in a suitable termination structure. ASEPS is well suited for the simulation of such termination structures.

As the computers became more powerful, the savings that ASEPS made possible became less important. It became possible, to simulate also larger device structures with general-purpose device simulators, such as the Pisces simulator developed by Stanford University, within reasonable time limits. For this reason, we stopped with the further development of ASEPS in the early ninties.

Historical Development

• ASEPS was first developed under a grant from Burr Brown (today Texas Instruments) in Tucson, Arizona. Burr Brown was one of the leading producers of linear power amplifiers, as they are e.g. being used in entertainment electronics. However, power amplifiers are also needed in communication systems, e.g. as part of satellites in a geostationary orbit, which are exposed to total dose ionizing radiation over long time periods. Burr Brown was interested in the development of ASEPS in that context. In the context of this project, ASEPS was being used for the simulation of reverse-biased bipolar power transistors.

• The development was later continued in several projects sponsored by the U.S. Defense Nuclear Agency (DNA). In these research projects, the main emphasis was the design of suitable termination structures for radiation-hardened power-MOSFET transistors that should protect these devices against an electromagnetic pulse (EMP).

• Also NASA was highly interested in our research results. Especially for missions to the inner solar system (planets Mercury and Venus), radiation-hardened power transistors are of great importance, as the space craft is exposed to a much larger total dose of ionizing radiation during such missions.

Most Important Publications

1. Wu, Q.M., and F.E. Cellier (1986), Simulation of High-Voltage Bipolar Devices in the Neighborhood of Breakdown, Mathematics and Computers in Simulation, 28, pp.271-284.

2. Wu, Q.M., C.M. Yen, and F.E. Cellier (1989), Analysis of Breakdown Phenomena in High-Voltage Bipolar Devices, Transactions of SCS, 6(1), pp.43-60.

3. Davis, K.R., R.D. Schrimpf, F.E. Cellier, K.F. Galloway, D.I. Burton, and C.F. Wheatley, Jr. (1989), The Effects of Ionizing Radiation on Power-MOSFET Termination Structures, IEEE Trans. Nuclear Science, 36(6), pp.2104-2109.

4. Kosier, S.L., R.D. Schrimpf, F.E. Cellier, and K.F. Galloway (1990), The Effects of Ionizing Radiation on the Breakdown Voltage of P-Channel Power MOSFETs, IEEE Trans. Nuclear Science, 37(6), pp.2076-2082.

5. Kosier, S.L., R.D. Schrimpf, K.F. Galloway, and F.E. Cellier (1991), Predicting Worst-Case Charge Buildup in Power-Device Field Oxides, IEEE Trans. Nuclear Science, 38(6), pp.1383-1390.

Sponsors

• Burr Brown, Inc.
• U.S. Defense Nuclear Agency

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