Punch-through Research Articles

Comparison of the Punch-Through and Non-Punch-Through IGT Structures

The insulated gate transistor (IGT) has been modeled as a wide-base bipolar junction transistor (BJT) driven by a MOSFET. Therefore, the vertical wide-base BJT structure influences the following IGT characteristics: 1) the forward current-voltage characteristics, 2) the fall time/forward-voltage drop trade-offs, 3) the high-temperature blocking, and 4) the turn-off current tail. An IGT with punch-through (PT) BJT yields lower forward voltage than that of an IGT with non-punch-through (NPT) BJT due to the thinner base of the PT BJT structure. The punch-through IGT has lower off-state (leakage) current and also shorter turn-off current tail due to lower current gain of a PT BJT than that of an NPT BJT. Both PT and NPT IGT's have large safe operation areas.

Characteristics of metal/tunnel-oxide/N/P + silicon switching devices—I : Effects of device geometry and fabrication processes

A systematic experimental study of metal/tunnel-oxide/ N/P + (MISS) devices is presented. Measurements on two-terminal devices suggest that the current-voltage characteristics are strongly dependent on tunnel-oxide area. Based on this data, it is concluded that this phenomenon is a result of current fringing which is expected to dominate for small-area devices (i.e. large perimeter-to-area ratio PAR). This is confirmed by measurements on devices with a constant area but varying PAR. Furthermore, the above observations are consistent with the regenerative feedback mechanism (responsible for initiating the switching process) being dependent on PAR. As a consequence of the results presented in this paper, the punch-through (PT) mode of operation described by Simmons et al.[1–3] is put into perspective. The conditions necessary for ideal PT switching to occur are clearly defined in terms of device parameters; in particular, area and area-to-perimeter ratio, tunnel-oxide thickness, and the effects of fabrication processes. Furthermore, it is shown that the current-voltage characteristic of the MISS device can be influenced by the field-oxide thickness and the frequency of the measurement signal. All the above-mentioned factors will determine whether ideal punch-through behaviour is observed.