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Fabrication of Suspended Nanowire Structures
Jason Mast & Xuan Gao
Summer 2009 REU Program at Case Western Reserve University
Introduction Nano == 1 / billion Nanometer == 1 meter / billion
Nanowire == wire with diameter between 1-100
nm
Suspended Nanowire == A nanowire suspended
over a gap.
Top – Nanowire on substrate
Bottom – Nanowire suspended over
gapBlack == MetalGreen == NanowireGray == Si/SiO2 substrate
Applications
Cell Device
Biology & MedicineElectrical Circuits
ω ω'
Sensors
Goals
1. Fabricate suspended nanowire devices- Simple but not easy.
2. Test the devices and look at the I-V curves.
- Should be different because the substrate (read heat sink) is not in contact with the wire.
Method IBasic Idea
1. Carve trenches out of top SiO2 layer.2. Drop nanowires over the trenches.3. Evaporate metallic contact pads.
Step 1 - Start
Blue == 100 nm SiO2 Gray == Silicon
Step 2 – Spin Coat Photoresist
Photoresist layers act like sacrificial layers. We use them to mold our devices.
Purple == LOR-3A Yellow == S 1805
Step 3 – Carve out Trenchesi. Place wafer under photomask, and expose the sample to UV light.
ii. Submerge in CD-26. Iiii. Submerge in HF for 60 sec.
Top View
Rate ~ 1 nm / sec
Step 4 – Drop nanowires
This can be done using either wet or dry transfer.
Step 5 – Contact Padsi. Expose 2nd pattern to UV light.
ii. Submerge in CD-26 for 60 sec.
Step 5 - cont.
Iiii. Evaporate metal (5 nm Ti & then 50 nm Al).
Different shades of gray represent different elevations of metal.
iv. Let the wafer sit in Remover PG overnight.
Method IIBasic Ideas
1. Embed nanowires between layers of photoresist.2. Create metallic contacts.
Step 1 – Get Started
Blue == 100 nm SiO2 Gray == Silicon
Step 2 – Spin coat photoresist
Yellow == Photoresist
Step 3 – Drop nanowires
Green == Nanowires
Step 4 – Spin coat photoresist
Nanowires are now embedded between two layers of photoresist.
Step 5 – Contact Pads
i. Place under photomask, and expose to UV light.
ii. Submerge in CD-26 for 60 sec.
Step 5 - cont
Iiii. Evaporate metal (5 nm Ti & 300 nm Al).
vi. Submerge in Remover PG overnight.
Results – Method I
I was able to perform alignment.
However, alignment was far too complicated to implement.
Results – Method II
I was able to get suspended nanowire structures.
I was able to get a few I-V curves, and a resistance measurement.
AcknowledgmentsSpecial Thanks To: Case Western Reserve University Physics Department National Science Foundation Bob Mike McDonald Professor Kash Reza Sharghi-Moshtaghin
NSF REU grant DMR-0850037