Bipolar Mode FET Research Articles

Modeling of the Steady State and Switching Characteristics of a Normally Off 4H-SiC Trench Bipolar-Mode FET

The electrical characteristics of a normally off 4H-silicon carbide (SiC) bipolar-mode FET are investigated by means of a careful design activity and an intensive simulation study useful for a first-time-ever realization of this device in SiC. Specific physical models and parameters strictly related to the presently available 4H-SiC technology are taken into account. The device basically consists of a trench vertical JFET operating in the bipolar mode that takes full advantage of the superior material properties. A drain-current density up to 500 A/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> , a forced current gain on the order of 50, and a specific on-resistance as low as 1.3 mΩ·cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> are calculated for a 1.3-kV blocking voltage device. The turn-off delay is on the order of a few nanoseconds. The presented analysis is supported by experimental results on the p-i-n diodes embedded in the device structure.

Steady-State Analysis of a Normally-Off 4H-SiC Trench Bipolar-Mode FET

The steady state characteristics of a normally-off 4H-SiC Bipolar Mode FET (BMFET) with a low on-resistance are investigated in a wide range of currents and temperatures by means of an intensive numerical simulation study which clarifies what are the main design constraints. Specific physical models and parameters strictly related to the presently available 4H-SiC technology are carefully taken into account. A drain forward current density up to 500 A/cm2, a specific on-resistance lower than 2 mΩ∙cm2 and a current gain in the order of a few tens are calculated. The blocking voltage is in excess of 1.3 kV with a low leakage current. These results are compared with the experimental data measured in the same test conditions of another SiC power device already introduced to the market.

A lateral trench-MOS bipolar-mode FET on silicon-on-insulator

A new lateral trench-MOS bipolar-mode FET, which shows the normally-off characteristics, is proposed and verified by device simulation. The n-channel region is pinched off by a trench MOS structure of which the electrode is p-type silicon and the potential is fixed to the ground. The channel withstands up to the avalanche condition at the drain side. The current gain of the LTBMFET is improved without sacrificing the breakdown voltage and leakage current when compared with the conventional LBMFET.

Ion-implanted normally-off GaAs bipolar-mode FET (BMFET) for application in a wide temperature range

First results of a normally-off GaAs bipolar-mode field effect transistor (BMFET) produced by ion implantation into an epitaxial material are presented. The devices show extreme temperature stability of drain current, current gain, on-resistance and switching times up to and were still operational at . Changes in drain current can be limited to -2%/100 K and small-signal current gain varies by as little as -4%/100 K in the whole temperature range. Although they have characteristics like bipolar transistors, BMFETs have the great advantage of a decrease in drain current and current gain with increasing temperature so that self-heating does not occur up to a limiting temperature. The influence of the number of source fingers is examined. In addition to the DC properties, switching behaviour is presented in a wide temperature range and shows almost no degradation.

The bipolar mode FET: a new power device combining FET with BJT operation

In this paper the features of power BMFETs are presented. Characteristics in the off and on states are discussed for realistic cell structures, and the effect of the gaussian doping profile of the surface gate region on the blocking voltage is discussed for new BMFET structures halfway between standard vertical JFET and power BJTs. A comparative analysis with a standard power bipolar transistor of comparable geometry and doping shows that the new BMFET has higher current ratings at breakdown, larger current gain, does not suffer from current crowding phenomena and has lower saturation voltage.

Two-dimensional analysis of the I- V characteristics of normally-off bipolar-mode FET devices

On the basis of the physical picture obtained by a detailed two-dimensional numerical simulation, an analytical model is developed for the I- V characteristics of a normally-off bipolar-mode FET structure. The numerical results show that the device has basically two modes of operation. When the minority-carrier injection from the gate is negligible, the device operation is governed by the modulation of the potential barrier in the channel due to the gate and drain voltages. This gives rise to an exponential shape of the I- V characteristics in the subthreshold regime, while for larger drain currents a transition to a triodelike shape takes place. The second mode of operation is due to the injection of minority carriers from the gate. This bipolar mode of operation is modeled according to a regional approximation method. The limits of the proposed quasi one-dimensional analysis are discussed by comparisons with the two-dimensional numerical results. The comprehensive analytical model obtained gives results in very good agreement with the numerical simulations and can be used to assess the influence of the various geometrical and physical parameters on the performances of the device.

Performance analysis of a bipolar mode FET (BMFET) with normally off characteristics

The fabrication and characterization of a family of power bipolar-mode junction FETs (BMFETs) are reported. Blocking voltages up to 1000 V or currents up to 18 A (corresponding to 800 A/cm/sup 2/) have been obtained. The experimental results are used to get an insight into the physics of BMFET operation and to extract the basic design criteria for these structures. The performance of the BMFET is compared with that of the bipolar transistor, showing it to be superior. >