Slide #1

MESA Isolation

Source-Drain Contact

DEPOSITION

Schottky Contact DEPOSITION

Bonding Pad

DEPOSITION

Top Cantilever

OUTLINE ETCH

BACK POCKET ETCH

All the cantilever fabrication processes are performed in MiRC, Georgia Tech

Sacrificial layer

Forms cantilever thickness

Slide #2

MESA Isolation

Top Cantilever

OUTLINE ETCH

Source-Drain Contact

DEPOSITION

Schottky Contact

DEPOSITION

Bonding Pad

DEPOSITION

BACK POCKET ETCH

35m x 35 m MESA

Height: 200 nm

Si

GaN

GaN etching by Plasma Therm ICP Etcher

Slide #3

MESA Isolation

Ohmic Contact DEPOSITION

Schottky Contact DEPOSITION

Bonding Pad

DEPOSITION

Top Cantilever

OUTLINE ETCH

BACK POCKET ETCH

Defines the cantilever outline.

GaN etching by ICP (Inductively Coupled Plasma) Etcher

350 m

50 m

Slide #4

Metal Stack: Ti(20nm)/Al(100nm)/Ti(45nm)/Au(55nm)

Annealing: 800C for 60s in N2

MESA Isolation

Ohmic Contact DEPOSITION

Schottky Contact DEPOSITION

Bonding Pad

DEPOSITION

Top Cantilever

OUTLINE ETCH

BACK POCKET ETCH

Source and Drain

Slide #

Metal Stack: Ni(25nm)/Au(375nm)

MESA Isolation

Ohmic Contact DEPOSITION

Schottky Contact DEPOSITION

Bonding Pad

DEPOSITION

Top Cantilever

OUTLINE ETCH

BACK POCKET ETCH

5

Gate

Slide #6

Bonding pads

Metal Stack: Ti(20nm)/Au(150nm)

MESA Isolation

Ohmic Contact DEPOSITION

Schottky Contact DEPOSITION

Bonding Pad

DEPOSITION

Top Cantilever

OUTLINE ETCH

BACK POCKET ETCH

Si

Au

GaN

Slide #7

Anisotropic etch: Through wafer back Si etch (Bosch process)

Released cantilever

MESA Isolation

Ohmic Contact DEPOSITION

Schottky Contact DEPOSITION

Bonding Pad

DEPOSITION

Top Cantilever

OUTLINE ETCH

BACK POCKET ETCH

1.4 cm

Samples automatically diced

Slide #8

Slide #9

• The piezoresistive effect describe the changing resistivity of a material due to applied applied stress.

• The piezoresistive effect differs from the piezoelectric effect. In contrast to the piezoelectric effect, the piezoresistive effect only causes a change in electrical resistance; it does not produce an electric potential like the former.

• The piezoresistive effect can be due to dimensional changes and/or mobility changes (due to effective mass changes) like in Si.

• Piezoresistive effect is more “dc” i.e. the effect does not disappear after the cause is removed unlike the piezoelectric effect which is more transient due to leakage resistor.

Slide #10

Problem 1: Assume the transfer function of an accelerometer to be given as: Vout = 2.0 + (Accl. x 25 mV/g). Assume that the noise spectral density is 150 µV/Hz. This sensor is used in a car where it is necessary to have a reading every 100 ms.

(a)What is the sensitivity of the sensor?(b)What is the noise in the sensor output?(c)What is the input signal resolution of the sensor?(d)Describe the operation of an accelerometer that utilizes an inertial mass.

Slide #11

Problem 2: Consider piezoelectric power generation from soldier walking/running. Assume the soldier weighs 100 Kg and half of the body weight falls on the area of the PZT generator which is 40 cm2. If he runs at 5 m/s and has a step length of 0.5 m, calculate the average power generated by the soldier.

Given: d11 = 289 pC/N, and PZT layer thickness is 50 µm, and dielectric constant of 1500. Assume all the peizo-electrically generated charge by each step is dissipated before the next as he powers a small headlamp with the piezo generator.

Slide #12

Problem 3: Consider an AlGaN/GaN heterostructure with 35% Al composition.(i)What are the spontaneous polarizations in the AlGaN and GaN layers?(ii)What is the piezoelectric polarization in the AlGaN and GaN layers?(iii)What would be the fixed polarization charge at the interface of AlGaN/GaN with 35% Al composition?(iv)How will the polarization charge change if this structure is used to make a cantilever, and the stress generated due to bending is 0.05% at the interface. For simplicity only consider the strain to change at the interface.

Slide #13

Problem 4: Consider a rectangular Hall effect sensor made of GaAs semiconductor having length and width of 4 and 10 mm and thickness of 2 µm. If the mobility and carrier densities in the sensor chip are 10000 cm2/Vs and 1017 cm-3 , respectively, calculate the sensitivity of the Hall sensor at an applied voltage of 10 V.Mention one advantage and one disadvantage of a Hall effect sensor.

Slide #14

Problem 5: (a)Explain a sensing technology to determine the height of water level in a glass. (b)If the glass in now held under a tap, suggest a sensing strategy to fill the glass automatically to a certain height