Microwave Transistors

Abstract

Features of disigning field and bipolar transistors in the microwave range are considered. The main attention is paid to a field effect transistor with a Schottky barrier control on gallium arsenide. Equivalent schemes, physical-topological models and temperature models are presented. Features of functioning, parameters and characteristics are discussed. The noise model is analized.

Advancement Questions

• 1. What physical factors limit the speed of field and bipolar transistors?

• 2. Why is gallium arsenide preferred when choosing materials?

• 3. Illustrate the “genealogical” connection between field and bipolar transistors. Include a vacuum triode in the structures under consideration.

• 4. Compare the performance of different types of transistors.

• 5. Draw a cross section of the planar FT. Why does the FT need a buffer layer?

• 6. How can the power of the FT be increased?

• 7. Draw the input and output characteristics of the FT. How do you define differential parameters? What is the difference between the differential parameters and the small-signal parameters of the equivalent circuit?

• 8. Draw equivalent circuit of the FT and find dependes of its parameters from the physico-topological parameters of the structure. What kind of circuits do you know? What is the cutoff frequency? What is the maximum?

• 9. What is the physical meaning of scattering parameters? How are scattering parameters related to the parameters of the equivalent circuit?

• 10. What are the main assumptions in the Shockley model? Why do rough approximations give acceptable results? What is the local-field approximation?

• 11. What is the difference between the Shockley model and the model of two regions?

• 12. What are the main points of the transistor temperature model? Explain the effect of super-velocity.

• 13. Explain the FT operating principle from the viewpoint of the temperature model. Draw the electric field distribution and the electron temperature distribution. What is the shape of the depletion layer and the current channel?

• 14. What is the nature (sources) of noise in a MESFET? Why do the transistors have small noises, while the charge carriers in the current channel have a high electron temperature?

• 15. Explain the impedance field method when calculating the noise of a FT.

• 16. How do device noise parameters depend on the power mode?

• 17. What is the structure of a HEMT? Why does it have a high steepness?

• 18. What is the advantage of using modern materials: GaN, SiC, and C?

• 19. Compare the load characteristics of transistors made of different semiconductors.

• 20. Draw structure of the classical microwave bipolar transistor. What are the doping levels of the main regions? What are the ways to increase the working frequency  of BT?

• 21. Show the relationship of the equivalent circuit elements with the structure of the device. How are the cutoff and maximum frequency of BT determined?

• 22. What is the structure of a transistor with a wide-band emitter? What is the efficiency of the emitter?

• 23. Explain the frequency response of BT.

• 24. What is the difference between hybrid and monolithic microwave IC?