The power bipolar junction transistor (PBJT) is investigated and modeled. Particular interest is concentrated on the injection charge in the collector layer that dominates the large-signal characteristics of the device. Based on the semiconductor physics, ordinary differential equations describing the injection charge are derived. These equations take into account the recombination, charging, and discharging processes in the collector layer. A network model for the PBJT is derived by adding these equations to a standard model. This model is implemented in the IG-SPICE language. The static behavior, such as the quasi-saturation, and the dynamic behavior, including turn-off under the strong drive condition, can be simulated and analyzed. The simulation correlates well with the measurement. >

A power bipolar junction transistor model describing the static and the dynamic behavior

It is shown that the apparent bandgap narrowing Delta E/sub g//sup app/ in heavily doped silicon, deduced from the electrical measurements on bipolar transistors using minority-carrier mobility values, is consistent with the values extracted from the luminescence data. Using an empirical fit to this Delta E/sub g//sup app/ as a function of doping and the lifetime model applicable to heavily doped diffused layers, it is demonstrated by numerically computing the current gain of n/sup +/-p- nu -n/sup +/ transistors that the experimental current gain can be predicted with excellent accuracy. Using these models for estimating the hole current injected into the heavily doped emitter region, it is shown that the observed dependence of the collector lifetime of high-voltage transistors on the parameters of the emitter region can be adequately explained. High-voltage n/sup +/-p- nu -n/sup +/ transistors having different emitter junction depths and emitter surface doping concentrations are studied, and the experimental results are compared to theoretical calculations of current gain and collector lifetime. >

The effects of emitter region recombination and bandgap narrowing on the current gain and the collector lifetime of high-voltage bipolar transistors

A novel method of measuring the collector recombination lifetime, which is independent of emitter effects, is presented by extending the quasi-saturation analysis of high-voltage bipolar transistors to the high-current-density regime. The technique is supported by theory, and experimental results are presented on transistors fabricated with different emitter properties. This is a nondestructive method and gives the lifetime values at the current densities normally encountered when the transistor is in actual operation. The values for the collector recombination lifetime obtained by the present method are independent of the properties of the emitter region. >

Collector recombination lifetime from the quasi-saturation analysis of high-voltage bipolar transistors

Based on an extensive two-dimensional process and device simulation studies, a new n+-p-n-n+ vertical submicrometer bipolar junction transistor with a three-zone step doped lateral collector (VSLC) structure is presented. It is demonstrated for the first time that the breakdown voltage of the thin-film (<0.5 mum) bipolar transistors can be enhanced significantly by using a combination of a vertical thin base and the VSLC structure. The proposed VSLC structure exhibits: 1) excellent output characteristics; 2) diminished quasi-saturation; 3) improved reliability against self-heating effect; and 4) enhanced breakdown voltage as high as 60% more than that of the conventional thin-film lateral bipolar transistor (LBT) on silicon-on-insulator. It also obviates the difficulties associated with the formation of a thin base in LBTs

https://web.iitd.ac.in/~mamidala/HTMLobj-611/TDMR_06_06_SDRoy.pdf

Enhanced breakdown voltage, diminished quasi-saturation, and self-heating effects in SOI thin-film bipolar transistors for improved reliability: a TCAD simulation study

The advanced bipolar transistor operating in the quasi-saturation region has been modeled, including collector current spreading effects. It is shown that the multidimensional collector current spreading, resulting from high carrier concentration gradient in the collector, ameliorates quasi-saturation effects in the d.c. and transient operation. The mechanism of collector spreading is investigated by physical device simulations. SPICE circuit simulations employing the collector spreading model are compared with measurements and are found to be in excellent agreement.

Circuit modeling of collector current spreading effects in quasi-saturation for advanced bipolar transistors

High-voltage power transistor operating in the quasi-saturation region is analyzed taking into account the effects of the injection of holes into the collector and the back injection of the electrons from the collector into the base. It is shown that the collector recombination lifetime τ ν plays an important role on the power transistor characteristics. Experimental results available in the literature on the output characteristics and the injection level dependence of current gain of transistors agree very well with the analysis presented in this paper. It is also shown that the h FE I C product in the quasi-saturation region depends upon the collector region lifetime τ ν .

V. Ramasubramanian

Papers

The effects of collector lifetime on the characteristics of high-voltage power transistors operating in the quasi-saturation region