Transcript Schottky Contact DEPOSITION

MESA Isolation
Top Cantilever
OUTLINE ETCH
Source-Drain Contact
DEPOSITION
Forms cantilever
thickness
Schottky Contact
DEPOSITION
Sacrificial layer
Bonding Pad
DEPOSITION
  All the cantilever fabrication processes are performed in MiRC, Georgia Tech
BACK POCKET ETCH
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MESA Isolation
Top Cantilever
OUTLINE ETCH
Source-Drain Contact
DEPOSITION
GaN
Si
Schottky Contact
DEPOSITION
GaN etching by Plasma Therm ICP Etcher
35m x 35 m MESA
Height: 200 nm
Bonding Pad
DEPOSITION
BACK POCKET ETCH
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MESA Isolation
Top Cantilever
OUTLINE ETCH
Ohmic Contact DEPOSITION
350 m
50 m
Schottky Contact
DEPOSITION
GaN etching by ICP (Inductively Coupled Plasma) Etcher
Bonding Pad
DEPOSITION
Defines the cantilever outline.
BACK POCKET ETCH
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MESA Isolation
Top Cantilever
OUTLINE ETCH
Source and Drain
Ohmic Contact DEPOSITION
Schottky Contact
DEPOSITION
Metal Stack: Ti(20nm)/Al(100nm)/Ti(45nm)/Au(55nm)

Annealing: 800 C for 60s in N2
Bonding Pad
DEPOSITION
BACK POCKET ETCH
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MESA Isolation
Top Cantilever
OUTLINE ETCH
Gate
Ohmic Contact DEPOSITION
Schottky Contact
DEPOSITION
Metal Stack: Ni(25nm)/Au(375nm)
Bonding Pad
DEPOSITION
BACK POCKET ETCH
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MESA Isolation
Top Cantilever
OUTLINE ETCH
Bonding pads
Ohmic Contact DEPOSITION
Schottky Contact
DEPOSITION
Metal Stack: Ti(20nm)/Au(150nm)
Au
Bonding Pad
DEPOSITION
GaN
Si
BACK POCKET ETCH
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MESA Isolation
Top Cantilever
OUTLINE ETCH
Released cantilever
Ohmic Contact DEPOSITION
Anisotropic etch: Through wafer back Si etch (Bosch process)
Schottky Contact
DEPOSITION
Bonding Pad
DEPOSITION
1.4 cm
BACK POCKET ETCH
Samples automatically diced
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• 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.
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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)
(b)
(c)
(d)
What is the sensitivity of the sensor?
What is the noise in the sensor output?
What is the input signal resolution of the sensor?
Describe the operation of an accelerometer that utilizes an inertial mass.
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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.
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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.
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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.
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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
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