Gridistor development for the microwave power region

Multichannel junction-gate field-effect transistors and their advantages were introduced in 1964 under the name Gridistor. This included both vertical and horizontal channel structures. They were developed in order to combine in the same device the advantages of field-effect and bipolar transistors. The horizontal channel structure had performance which was quite useful in the power VHF band, but it was clear that for the higher frequency and power region the vertical channel structure would be basically more suitable. However, to develop this structure for the microwave power region an exhaustive investigation had to be undertaken with a view toward eliminating its drawbacks, namely the relatively high grid resistance and also differential drain conductance. The first problem was solved by modifying the grid geometry and increasing the grid bulk impurity concentration, and the second by providing an appropriate gradation of the source and drain layer resistivities. Thus, with the usual technology and moderate grid fineness, but with optimized grid geometry, an operating frequency above 1 GHz was attained, f
max
being ∼5 GHz, with a frequency-power product of ∼5 GHz. W for a single-chip Gridistor. The features of the devices produced are discussed and a complete set of experimental results is provided. Finally, new developments now being initiated with the expectation of attaining in the near future an operating frequency of 8 GHz in the power region of 1 to 2 W are outlined. An anticipated structure, which will approach the ultimate limits of the Gridistor, is also discussed. This paper deals only with the experimental part of the problems concerning the Gridistor.