Gridistor
The gridistor is a variant of the junction field effect transistor with many channels created by gate electrodes arranged in a grid. Various designs of the grid transistor derived from the Tecnetron (also called Fieldtron ) were first described in 1964 by S. Teszner.
Structure and functionality
In the following, a gridistor with a vertical n-channel, that is to say perpendicularly through the substrate, is described. The starting point is a highly doped n-conductive silicon substrate on which a silicon dioxide layer is first created (thermal oxidation of silicon or chemical vapor deposition ). This is then structured, that is, removed locally in the form of a specific pattern and serves as a mask for the subsequent gas phase diffusion of boron into the substrate. The resulting lattice-shaped highly doped p-type (p + ) regions - the name Gridistor which derives (engl. Grid = dt. Grid ) - later form the gate and are framed by an equally doped region (necessary for the contacting of the gates). Then, as with the epitaxial transistor developed a few years earlier , the epitaxial deposition of a lightly doped n-conductive layer (1–2 Ω · cm) takes place, whereby the gate grid is now below the surface (“buried”). Two more diffusion steps then follow. On the one hand, a further boron diffusion across the epitaxial layer in order to contact the buried frame of the gate grid; on the other hand, a phosphorus diffusion in order to create a highly doped n-conductive area for the source or the surface of the epitaxial layer near the surface. Generate drain connection (see ohmic contact ). The other source or drain connection is located on the rear side of the highly doped substrate and does not require any additional generation of a highly doped area. The doping profile of the buried p + -doped regions also changes during the second and third diffusion step. With appropriate process management, an approximately circular cross-section of the p + regions can be achieved in the optimal case .
The functional principle of a gridistor corresponds to that of a normal junction transistor (see function in the article junction field effect transistor ), with the exception that there is not just one channel from source to drain, but a large number. If the gate electrode is not applied with a negative voltage, the channels are open and the behavior corresponds to that of an ohmic resistor. If, on the other hand, the grid-shaped gate electrode is subjected to a negative voltage, a space charge zone (RLZ) expands radially around the pn junctions to the substrate and narrows the channels (called centripetal striction ). At low voltages, however, the channel remains conductive, since the potential along the axis of symmetry between the gate electrodes has the value zero. Only when a certain voltage is reached is the channel pinch-off and is therefore no longer conductive. In this case, the two space charge zones touch and two pn junctions are formed between the source and drain that block the flow of current.
properties
According to Teszner, the gridistor is supposed to combine advantages of field effect and bipolar transistors of the time , which are based on the injection of minority charge carriers (such as the bipolar transistor). The field-controlled gridistor should correspond to the slope, operating frequency and output power of bipolar transistors of that time.
Other names and similar components
Teszner et al. describe various construction variants of a gridistor in their articles and patents. The course of the channel, the cross-sectional shape of the grid-shaped gate electrodes or the manner in which the gate electrode is connected are varied.
In addition, can also be found in the literature a number of similar devices, such as the field-controlled thyristor (Engl. Field-controlled thyristor , FCTh, more buried gate FCTh), field-terminated diode (FTD), static induction thyristor (SITh) or static induction transistor (SIT) should also correspond to the gridistor. However, the detailed descriptions sometimes deviate with regard to the doping zones or profiles used and it is unclear whether these inevitably use the lattice structure that is characteristic of the gridistor.
Patents
- Patent US3274461 : High frequency and power field effect transistor with mesh-like gate structure. Published on September 20, 1966 , inventor: Stanislas Teszner.
- Patent US3176192 : Integrated circuits comprising field-effect devices. Published March 30, 1965 , Inventors: Rene C. Sueur, Stanislas Teszner.
- Patent US3497777 : Multichannel field-effect semi-conductor device. Published on February 24, 1970 , inventor: Stanislas Teszner.
Individual evidence
- ↑ a b c S. Teszner: Gridistor development for the microwave power region . In: IEEE Transactions on Electron Devices . tape 19 , no. 3 , 1972, p. 355-364 , doi : 10.1109 / T-ED.1972.17425 .
- ↑ a b S. Teszner, R. Gicquel: Gridistor-A new field-effect device . In: Proceedings of the IEEE . tape 52 , no. 12 , 1964, pp. 1502-1513 , doi : 10.1109 / PROC.1964.3439 .
- ↑ E. Falck, W. Gerlach, M. Paissios: The blocking behavior of field-controlled thyristors (FCThs) . In: Archives for electrical engineering . tape 73 , no. 5 , 1990, pp. 343-352 , doi : 10.1007 / BF01574270 .
- ↑ J. Nishizawa, T. Terasaki, J. Shibata: Field-effect transistor versus analog transistor (static induction transistor) . In: IEEE Transactions on Electron Devices . tape 22 , no. 4 , 1975, p. 185-197 , doi : 10.1109 / T-ED.1975.18103 .