A study of frequency response in silicon heterojunction bipolar transistors with amorphous silicon emitters

A detailed physical model of amorphous silicon (aSi:H) is incorporated into a twodimensional device simulator to examine the frequency response limits of silicon heterojunction bipolar transistors (HBT's) with aSi:H emitters. The cutoff frequency is severely limited by the transit time in the emitter space charge region, due to the low electron drift mobility in aSi:H, to 98 MHz which compares poorly with the 37 GHz obtained for a silicon homojunction bipolar transistor with the same device structure. The effects of the amorphous heteroemitter material parameters (doping, electron drift mobility, defect density and interface state density) on frequency response are then examined to find the requirements for an amorphous heteroemitter material such that the HBT has better frequency response than the equivalent homojunction bipolar transistor. We find that an electron drift mobility of at least 100 cnr'V"'"1 is required in the amorphous heteroemitter and at a heteroemitter drift mobility of 350 cm2 · V1· s1 and heteroemitter doping of 5×1017 cm3, a maximum cutoff frequency of 52 GHz can be expected. © 1996 IEEE.

Analytic model for turn off in the silicon-on-insulator LIGBT

Lateral insulated gate bipolar transistors (LIGBTs) in silicon-on-insulator (SOI) show a unique turn off characteristic when compared to junction-isolated RESURF LIGBTs or vertical IGBTs. The turn off characteristic shows an extended `terrace' where, after the initial fast transient characteristic of IGBTs due to the loss of the electron current, the current stays almost at the same value for an extended period of time, before suddenly dropping to zero. In this paper, we show that this terrace arises because there is a value of LIGBT current during switch off where the rate of expansion of the depletion region with respect to the anode current is infinite. Once this level of anode current is approached, the depletion region starts to expand very rapidly, and is only stopped when it reaches the n-type buffer layer surrounding the anode. Once this happens, the current rapidly drops to zero. A quasi-static analytic model is derived to explain this behaviour. The analytically modelled turn off characteristic agrees well with that found by numerical simulation.

Simulated superior performance of superjuction bipolar transistors

This paper presents for the first time an investigation and comparison of the superjunction IGBT (SJBT) as proposed in [1,2] and the current state of art Field Stop IGBT [3,4]. Simulation results indicate the superior performance of the superjunction IGBT under switching conditions. For the same conditions, at a collector current density of 100A/cm2 and on-state voltage 1.6 V the switching off losses for a SJBT and Field-Stop IGBT are 1 and 4.5 mJ/cm 2 respectively. © 2006 IEEE.

200 v superjunction N-type lateral insulated-gate bipolar transistor with improved latch-up characteristics

This paper evaluates the technique used to improve the latching characteristics of the 200 V n-type superjunction (SJ) lateral insulated-gate bipolar transistor (LIGBT) on a partial silicon-on-insulator. SJ IGBT devices are more prone to latch-up than standard IGBTs due to the presence of a strong pnp transistor with the p layer serving as an effective collector of holes. The initial SJ LIGBT design latches at about 23 V with a gate voltage of 5 V with a forward voltage drop (VON) of 2 V at 300 Acm2. The latch-up current density is 1100 Acm2. The latest SJ LIGBT design shows an increase in latch-up voltage close to 100 V without a significant penalty in VON. The latest design shows a latch-up current density of 1195 A cm2. The enhanced robustness against static latch-up leads to a better forward bias safe operating area. © 1963-2012 IEEE.