1. EEE 490 Fall 2000, Dr. Thornton Hybrid Molecular MOS Transistor EEE 490 Final Presentation

2. EEE 490 Fall 2000, Dr. Thornton Project Overview The objective of this project was to modify a Silicon on Insulator (SOI) device to be sensitive to an environmental condition (light). The molecule that is used has to be sensitive to the desired environmental condition. When light hits the molecular layer, the molecule’s bonds are broken, and forms dipoles and creates additional charge on the silicon surface.

3. EEE 490 Fall 2000, Dr. Thornton Project Overview The threshold voltage is measured before the device comes in contact with light, and then after light hits the molecule on the device. The threshold voltage is different due to the change in surface potential generated by the effect of the light hitting the molecule.

4. EEE 490 Fall 2000, Dr. Thornton Silicon on Insulator Devices Silicon on Insulator (SOI) is a new technology that has a number of advantages over ordinary silicon technologies including: –SOI Devices are 25%-30% faster 1. –SOI Devices have less leakage current through the substrate due to the buried insulator layer 2. –SOI Devices have reduced parasictic capacitance 2. Source: 1. Why Silicon-on-Insulator, www.semiconductor.net/semiconductor/issues/issues/2000/200008/six0008io.asp 2. SOI technology, www.iee.et.tu-dresden.de/~graupner/off/soi0_e.html

5. EEE 490 Fall 2000, Dr. Thornton SOI Fabrication (Basic Steps) 1. Bare silicon wafer (for our case p-type). 2. High energy implant of oxygen atoms. 3. Source and Drain Boron implant. 4. Source, Drain, and Substrate contacts. 5. Addition of the molecular layer.

6. EEE 490 Fall 2000, Dr. Thornton Model of the Process

7. EEE 490 Fall 2000, Dr. Thornton Model of the Process

8. EEE 490 Fall 2000, Dr. Thornton Model of the Performance Linear Scale Log Scale

9. EEE 490 Fall 2000, Dr. Thornton Model of Molecular Layer To model the shift in threshold voltage we attempted it by two different methods: –applied a voltage at the gate region –put a fixed charge at the Silicon Dioxide/Silicon interface. Gate Voltage = 0.4V2E11 C of charge added

10. EEE 490 Fall 2000, Dr. Thornton Circuit We built an external circuit to measure the threshold voltage of the Transistor. –We used a modified Wilson Current Mirror.

11. EEE 490 Fall 2000, Dr. Thornton Circuit Output

12. EEE 490 Fall 2000, Dr. Thornton IV Characteristics Vd=10mV Linear ScaleLog Scale

13. EEE 490 Fall 2000, Dr. Thornton IV Characteristics Vd=100mV Linear ScaleLog Scale

14. EEE 490 Fall 2000, Dr. Thornton IV Characteristics Vd=1V Linear Scale Log Scale

15. EEE 490 Fall 2000, Dr. Thornton Molecule We used a an alkane, that is not light sensitive and an spiropyran, which will be responsible for creating a charge separated stable state when irradiated with light of the correct wavelength. –The alkane is a 16 carbon chain with a carboxylic acid at the end. –The spiropyran is a bicyclic system with a small chain with a carboxylic acid on one of the rings.

16. EEE 490 Fall 2000, Dr. Thornton Significance We were able to change the operational parameters of a MOS Transistor by using a light sensitive molecule. We were able to model the device and the device shift using commercial software. This may lead to more research being performed at ASU on a wide range of biosensors.

17. EEE 490 Fall 2000, Dr. Thornton Future Work Duplicate Results Fully characterize the light sensitive transistors. Find applications for this device, and devices with similar processing. Research other molecules, and apply them in much the same way.