![Page 1: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/1.jpg)
Fabrication of Suspended Nanowire Structures
Jason Mast & Xuan Gao
Summer 2009 REU Program at Case Western Reserve University
![Page 2: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/2.jpg)
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
![Page 3: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/3.jpg)
Applications
Cell Device
Biology & MedicineElectrical Circuits
ω ω'
Sensors
![Page 4: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/4.jpg)
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.
![Page 5: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/5.jpg)
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
![Page 6: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/6.jpg)
Step 2 – Spin Coat Photoresist
Photoresist layers act like sacrificial layers. We use them to mold our devices.
Purple == LOR-3A Yellow == S 1805
![Page 7: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/7.jpg)
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
![Page 8: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/8.jpg)
Step 4 – Drop nanowires
This can be done using either wet or dry transfer.
![Page 9: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/9.jpg)
Step 5 – Contact Padsi. Expose 2nd pattern to UV light.
ii. Submerge in CD-26 for 60 sec.
![Page 10: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/10.jpg)
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.
![Page 11: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/11.jpg)
Method IIBasic Ideas
1. Embed nanowires between layers of photoresist.2. Create metallic contacts.
Step 1 – Get Started
Blue == 100 nm SiO2 Gray == Silicon
![Page 12: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/12.jpg)
Step 2 – Spin coat photoresist
Yellow == Photoresist
Step 3 – Drop nanowires
Green == Nanowires
![Page 13: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/13.jpg)
Step 4 – Spin coat photoresist
Nanowires are now embedded between two layers of photoresist.
![Page 14: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/14.jpg)
Step 5 – Contact Pads
i. Place under photomask, and expose to UV light.
ii. Submerge in CD-26 for 60 sec.
![Page 15: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/15.jpg)
Step 5 - cont
Iiii. Evaporate metal (5 nm Ti & 300 nm Al).
vi. Submerge in Remover PG overnight.
![Page 16: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/16.jpg)
Results – Method I
I was able to perform alignment.
However, alignment was far too complicated to implement.
![Page 17: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/17.jpg)
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.
![Page 18: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/18.jpg)
![Page 19: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/19.jpg)
![Page 20: Fabrication of Suspended Nanowire Structures Jason Mast & Xuan Gao](https://reader036.vdocuments.net/reader036/viewer/2022070413/56814d40550346895dba666b/html5/thumbnails/20.jpg)
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