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 35  m 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: 800  C 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

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: V out = (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 cm 2. 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: d 11 = 289 pC/N, and PZT layer thickness is 50 µm, and dielectric constant of 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 cm 2 /Vs and 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