Mineo Katsueda

Thermal stability and secondary breakdown in planar power MOSFET's

The destructive secondary-breakdown mechanism of high-voltage n-channel power MOSFETs is discussed. A model is proposed in which the secondary breakdown is caused primarily by the negative-resistance effects of a parasitic bipolar transistor structure. The model suggests that destructive breakdown can be suppressed by a new no-surface-breakdown structure fabricated on a p-on p+epitaxial wafer. Power MOSFETs having this structure have been realized and are completely free from secondary breakdowns, as suggested by the model. In addition, experimental evidence for excellent thermal stability of the power MOSFET is given by infrared scanner measurements of the temperature rise in the chip compared with bipolar transistors. An n-channel planar power MOSFET with a 400-W power limitation at 220-V breakdown voltage and a maximum current of 12 A has been successfully fabricated.

A highly efficient 1.9-GHz Si high-power MOS amplifier

A 1.9-GHz Si power MOSFET with 50% power-added efficiency and 0.3-1.0 W output power at a 3-5 V supply voltage has been developed for use as a high-power amplifier in cellular telephones. This MOSFET achieves high efficiency and high-power gain at low supply voltage by using a 0.5-/spl mu/m gate power MOSFET with an Al-shorted metal-silicide/Si gate structure, which improves the cut-off frequency and reduces the on-state resistance.

Radiation effects on UHF power MOSFETs

The effects of ionizing radiation of UHF power MOSFETs are studied. It is found that a power MOSFET amplifier exhibits little change in output power and efficiency in the linear region, but it is seriously degraded in the saturation region. The reason for this degradation is an increase in on-resistance and a decrease in the maximum current, both caused by radiation-induced interface states. A MOSFET exposed to radiation while it is operating as an amplifier at 860 MHz has a different threshold voltage shift than one not operating at high-frequency. This phenomenon can be explained by the annealing effect of the high-frequency electric field across the gate. For improvement in radiation tolerance, a device with a thinner thermal oxide film on the offset region is proposed and discussed. >

High-frequency annealing effects on ionizing radiation response of MOSFET

The effects of high-frequency AC bias on the ionizing radiation response of MOSFETs are studied. Radiation-induced interface traps are annealed out during irradiation and postirradiation annealing when an AC bias is applied with a zero offset voltage. In addition, the recovery of 40-MHz-biased devices agreed with that of 860-MHz-biased ones for the same total number of alternating cycles of AC gate bias voltage. It is concluded that an alternating transition between inversion and accumulation caused by high-frequency AC bias is responsible, and the total number of transition cycles may be relevant for the annealing of radiation-induced interface traps. >