Triode-like Characteristics Research Articles

High-voltage junction-gate field-effect transistor with recessed gates

A new recessed-gate structure for vertical-channel junction field-effect transistors (JFET's) is described together with a self-aligned gate-source process developed to fabricate these devices. Using this technology, devices with groove depths ranging from 8 to 18 µm have been fabricated. The characteristics of these devices is described as a function of the groove depth. It has been found that the devices display pentode-like characteristics at low gate voltages and triode-like characteristics at high gate voltages. The blocking gain has been found to increase with groove depth. However, this is accompanied by an increase in the on-resistance and a decrease in the saturated drain current. Devices with gate breakdown voltages of up to 600 V have been fabricated with the recessed-gate structure. These high-voltage field-effect transistors (FET's) have a unity power gain cutoff frequency of 600 MHz and gate turn-off times of less than 25 ns.

MP-A2 Triode-like characteristics of short-channel MOSFET's in punch-through mode operation

MP-A2 Triode-like characteristics of short-channel MOSFET's in punch-through mode operation

A Two-Dimensional Computer Analysis of Triode-Like Characteristics of Short-Channel MOSFET's

Some new understandings on the triode-like behavior and the "punchthrough mode" operation of a short-channel MOSFET are obtained based on a two-dimensional computer simulation. The drain current of a MOSFET is essentially space-charge-limited, showing a shift from a pentode-like behavior to a triode-like behavior with decreasing (source-drain distance/gate oxide thickness) ratios which serve to manifest the relative modulations by the gate and the drain upon the channel conductivity. In a short-channel MOSFET, the triode-like behavior is more accentuated by a "punchthrough effect" due to a lowering of the potential barrier at the source by the drain field. The current thus resulted includes a gate-uncontrollable component flowing deep in the bulk, which is termed "punchthrough current" to distinguish it from the gate-controllable component characterizing the triode-like behavior. Optimized conditions for a device for reducing the "punchthrough current," are also described in detail.

A two-dimensional computer analysis of triode-like characteristics of short-channel MOSFET's

Some new understandings on the triode-like behavior and the "punchthrough mode" operation of a short-channel MOSFET are obtained based on a two-dimensional computer simulation. The drain current of a MOSFET is essentially space-charge-limited, showing a shift from a pentode-like behavior to a triode-like behavior with decreasing (source-drain distance/gate oxide thickness) ratios which serve to manifest the relative modulations by the gate and the drain upon the channel conductivity. In a short-channel MOSFET, the triode-like behavior is more accentuated by a "punchthrough effect" due to a lowering of the potential barrier at the source by the drain field. The current thus resulted includes a gate-uncontrollable component flowing deep in the bulk, which is termed "punchthrough current" to distinguish it from the gate-controllable component characterizing the triode-like behavior. Optimized conditions for a device for reducing the "punch-through current," are also described in detail.

A power junction gate field-effect transistor structure with high blocking gain

A new gate structure is described for vertical-channel power junction gate field-effect transistors (FET's). This gate structure has vertically walled gate regions extending perpendicular to the wafer surface. The structure is fabricated by using orientation-dependent silicon etching and selective vapor-phase epitaxial refill techniques. In comparison to previous gate structures made by planar diffusion, the vertically walled gate structure exhibits one order of magnitude improvement in blocking gain. This improvement in blocking gain has allowed the fabrication of devices having breakdown voltages above 400 V and a current-handling capability of more than 0.5 A with an on-resistance of 12 Ω. The devices are designed to exhibit pentode-like characteristics at low gate voltages and triode-like characteristics at large reverse gate bias voltages in order to obtain the observed high-power handling capability.

Submicron channel MOSFET's logic under punchthrough

The characteristics of n-channel MOSFETs that make use of the punchthrough current are considered in this paper. The current conduction mechanisms of the short channel MOSFET under the bias condition of punchthrough have been studied through the use of two-dimensional computer simulation. Experimental devices with channel lengths as short as 0.5 /spl mu/m were fabricated on a lightly doped substrate. Current-voltage curves of these devices showed pentode-like characteristics for smaller drain biases and triode-like characteristics for larger drain biases. A switching delay as small as 75 ps was obtained for a 13-stage ring oscillator composed of the submicron channel devices.

Optimum design of triode-like JFET's by two-dimensional computer simulation

Design criteria of triode-like JFET's are studied by fully utilizing two-dimensional numerical analysis. The current is caused by tlie carriers injected over a potential barrier in a depleted channel. In contrast to normal pentode-like FET'S, the drain field plays an important role reducing the barrier height and thus causing triode-like I-V characteristics. Triode-like characteristics depend strongly on device geometry. This operation can be realized only in short gate devices. The channel thickness a is an essential parameter in determining the operational mode. The devices operate as triodes or pentodes corresponding to thin or thick channels, respectively. If applied to low-resistance load direct-drive circuits, the mixed characteristics situated between the triode- and pentode-like ones, are more desirable when compared to pure triode-like ones, This is because of their low on-resistance and high ac power efficiency. The gate-drain distance l gd is also essential in determining breakdown voltage. The design criteria are discussed and an optimum design specified on the N D (channel doping)- a and N_{D} - l_{gd} planes with respect to triode-like characteristics, circuit application and breakdown phenomena. Calculated results are compared with experiments and good agreement is found without using any adjustable parameters. The present design criteria will be useful for designing triode-like JFET's.

Two-dimensional Analysis of Vertical Junction Gate FET's

Vertical junction gate FET's are new high power devices. They show triode-like characteristics which are different from conventional FET's. In this paper, triode-like operation of V-FET's is studied using two-dimensional numerical analysis. The analysis shows that the depletion of the channel by the gate potential is a prerequisite for triode-like operation. It also shows that the gate spacing d and gate-drain length lgd have a great influence on the operation of V-FET's. The transition from triode- to pentode-like characteristics is brought about by increasing d or lgd. Avalanche breakdown voltage depends strongly on the electric field distribution and is also a good problem of the two-dimensional analysis. Design criteria for V-FET's are discussed with respect to triode-like operation and breakdown.

Two-dimensional analysis of triode-like operation of junction gate FET's

Triode-like operation of junction gate FET's is analyzed by two-dimensional computer simulation. Triode-like characteristics are shown to appear with the channel normally off and the depletion layer reaching the drain electrode. Triode-like current arises from carrier injection from the source electrode into the depleted region. Triode-like operation is achieved without intrinsic material.

Carrier accumulation and space-charge-limited current flow in field-effect transistors

This paper reports an investigation of devices fabricated by lateral diffusion techniques which have non-uniform doping profiles along the channel. The application of a two-dimensional numerical method to a device model representing these devices shows carrier accumulation in the conductive channel. The increase of carrier concentration with the increasing drain-to-source voltages is caused by the interaction of the source and the drain N +-regions. This indicates the possibility of the space-charge-limited current which is a different conduction mechanism from that of the conventional devices. From the study of one-dimensional N +-N-N + structures, the length-to- L DE (extrinsic Debye length) ratio of the channel and the crossover voltage have been recognized as important parameters in realizing the space-charge-limited current. The drain characteristics of a device model with a small crossover voltage and a small length-to- L DE ratio are obtained by a simple analysis. Triode-like characteristics are found for this model as expected.

Transition from pentode- to triode-like characteristics in field effect transistors

It is shown with the use of the Geurst theory that field effect transistors should exhibit a transition from pentode-like to triode-like characteristics with increasing drain bias, corresponding to the approach of the pinch-off point to the source and to space-charge-limited injection from the source. The transition point is markedly geometry-dependent and occurs at lower voltages the smaller the ratio of channel length/channel (or insulator)_thickness. The theoretical results permit clarification of the origin of the widely diverse characteristics observed in multi-channel field effect transistors.