Gaas Metal Oxide Semiconductor Field Effect Transistors Fabricated with Low Temperature

To keep y’all up with what’s going on in the transistor world we have collected a few articles for you.

GaAs Metal Oxide Semiconductor Field Effect Transistors Fabricated with low Temperature Liquid Phase Deposited SiO2 in a Microgravity and High Pressure Nitrogen Chamber.

The GaAs field effect transistor with insulated gate design is a well known technology but development has hit a wall on high frequency and low noise capability. SiO2 films are still widely applied in use as insulating material in the fabrication of semiconductor devices.

The vapor pressure of Arsenic is so high that Arsenic sublimation from GaAs occurs. The result of this is that the high temperature oxidation produces nonstoichiometric oxide films. To counter this we recommend a low temperature (30 to 60  C) Liquid Phase Deposition by which SiO2films can be deposited on substrates during immersion of the substrates in a Boric Acid solution.

As expected, the microgravity environment caused the substrate material to become porous. This was overcome by working in a high pressure nitrogen environment. The microgravity environment was preferable to prevent inconsistent impurity settling while the substrate is in the liquid state of manufacturing.

In this study we fabricated GaAs MOSFET transistors of both N-Channel and P-Channel structure in individual transistors as well as basic analog and digital integrated circuits. The basic transistor structure was 4 m gate length. The SiO2 layer formed at a predicted rate of 60 /h (Angstroms per hour).

I didn’t note where I got this article from. What they are saying is that we have run into a wall on the highest operating frequency and noise level in Gallium Arsenide transistors. As operating frequency got higher (50 GHz area) we lost gain capability and the transistor itself generated a lot of noise.

Trying manufacturing processes at higher heat they found out that the manufacturing process itself had flaws. At higher temperatures the Arsenic separated out of the liquid material. Not obvious here is the fact that they were doing these experiments in the micro-gravity of space. Now you know what those experiments are they do in the Space Station. In the micro-gravity of space the results were a spongy silicon. A bad thing. Here on Earth the pull of gravity kept the liquid solution at a good solid structure. They expected, and confirmed, that micro-gravity caused air bubbles in the liquid. To prevent this they melted the Gallium Arsenide solution in a high pressure Nitrogen environment. While working in a gravity environment had one benefit it also created a problem. We get inconsistent settling of the particles as they come from liquid to solid state. The heavier elements settled toward the bottom of the pot quicker that lighter elements. Thus the desire to create semiconductors in micro-gravity. Now you know how they dealt with the problems.

The result is transistors in the 4 m size capable of hundreds of GHz.