今天开始，推出一个系列的“MMIC问答”，基本包括MMIC设计的方方面面。当然，这个高度不是我所能达到的，我只是做做打字员，借花献佛。再次强烈推荐Steve Marsh著《Practical MMIC Design》。

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Chapter 2: Component Technology and Foundry Choice

Questions:

1. What characteristics of the semiconductors material determine the frequency range over which it can be used for producing MMICs?

2. Which semiconductor substrate materials exhibit a wide bandgap, making them suitable for high-output power applications?

3. What are the typical gate voltage and drain current bias settings for a GaAs MESFET?

4. What is the bias voltage required between the base and emitter contacts of a typical silicon bipolar transistor to overcome the built-in junction potential and switch the transistor fully on?

5. Why must the electrical connections between components on an MMIC be treated as transmission lines?

6. How does the characteristic impedance of a microstrip transmission line vary as the width of the track is increased, and is this due to the track looking more inductive or capative?

7. Following figure shows the section and plan view of a nichrome resistor. If the nichrome film has a resistivity of 50-Ohm/Square, what is the resistance of this resistor?



8. Following figure shows the section and plan view of polyimide and silicon nitride MIM capacitors. Given that the silicon nitride has a thickness of 1200ai and a dielectric constant of 7e-11 and the polyimide thickness is 1.5um and has a dielectric constant of 3.6e-11, what is the capacitance of a 30um-square silicon nitride capacitor, and how much greater capacitance does it have than a 30um-square polyimide capacitor?



9. What limits the dc current carrying capacitance of a spiral inductor?

10. When are stacked spiral inductors used?

Answers:

1. The electron peak velocity and the electron mobility.

2. Silicon carbide and gallium nitride.

3. Gate voltage of -0.5V and drain current of half the drain saturation current (Idss/2).

4. Vbe forward biased at typically +0.7V.

5. The distance between components on an MMIC can approach significant fractions of the signal wavelength, so the phase and amplitude vary along the connections as functions of time and distance.

6. The characteristic impedance becomes lower as the track width is increased because the track looks more capacitive.

7. 125-Ohm.

8. The 30-um silicon nitride capacitor is 0.5pF, which is 25 times larger than the same size polyimide capacitor.

9. The width of the metal track used for constructing the spiral inductor.

10. At RF and low microwave frequencies.