Question

Provide a description of the materials selection for the following micro-sensors/actuators:

1.) substrates and wafers

2.) silicon compounds such as dioxide, carbide, nitride, and polycrystalline

3.) silicon piezoelectric

4.) gallium arsenide

5.) piezoelectric crystals

6.) polymers

7.) films

Answer 1

Ans1: Silicon is most commonly material used as a substrate.

Properties of silicon as a substrate are as follows:

1. Mechanically stable
2. High melting point (1400 C)
3. Ideal structural material with young modulus close to steel and light weight as a compared to Aluminium.

Wafers material can be silicon or single crystalline material like quartz and gallium arsenide.

Ans2:

Silicon oxide in microsystems:

1) Acts as a thermal and electric insulator

2) Acts as a mask for the etching process of silicon substrates

3) Acts as a sacrificial layer for surface micromachining.

Silicon carbide (SiC) in microsystems:

1. Chemically stable and dimensional sturdy at high temperatures.
2. Strong resistance against oxidation at very high temperatures

Silicon nitride

1. Excellent barrier against diffusion of water and other ions.
2. Strong resistance against oxidation.
3. Acts as a mask for deep etching.
4. High-strength electric insulators.

Silicon Polycrystalline

1. Excellent material for surface micromachining
2. Good material for ohmic contacts

Ans 4:

Gallium arsenide (GaAs):

1. Basically, a semiconductor compound.
2. Consist of equal numbers of gallium and arsenic atoms.
3. Complicated lattice structure.
4. Excellent material for integration of electronic and photonic devices.
5. High mobility of electrons as compares to other semiconducting materials, thus quiet easier for current flow.

Ans 5:

Piezoelectric crystal:

Piezoelectric crystals are most commonly used materials in microsystems.

Are solid crystal compounds that can produce a voltage when a mechanical force is applied along their faces.

Generates high voltage with the application of high compressive stress.

Use as pressure sensors for accelerometer.

Ans 6

Polymers:

1. Consists of long chain of hydrocarbons.
2. Has low mechanical strength, low melting point, and poor electrical conductivity.
3. Good coating agent
4. Used as electric insulator

Ans 7

Films:

1. Developed by Langmuir and Blodgett thus commonly known as LB films.
2. Good materials having ferro (magnetic), pyro (heat-generating), and piezoelectric properties.
3. ideal materials for microsensors and optoelectronic devices.