This presentation will describe my research here during SULI s summer 2012 program. My project was to fabricate nano-film capacitors. I was given this project because the Linac Coherent Light Source s sensors plan to upgrade to capture 50,000 x- rays/pixel/frame instead of 3,000. New smaller capacitors with a larger capacitance was needed to keep the voltage gain under the saturation level of the Op-Amp in the integrated circuit. This presentation will explain the process in which I fabricated the capacitors.
Frankie Reed University of Michigan 2012 SULI Program Performed at SLAC Mentor: Christopher Kenney
Intro Why Nano-Film Capacitors? The Process The Actual Process Conclusion and Acknowledgements
Au A capacitor of one farad (F) means that one coulomb (C) of charge on each plate causes one volt (V) across the device. V=Q/C
Linear Coherent Light Source (LCLS) examines materials or atoms by taking x-rays Sensors at LCLS now can capture 3000 x- rays/pixel/frame (1 x-ray s energy is on the order of 8 kev) In the future LCLS would like to be able to capture 50,000 x-rays/pixel/frame in a sensor What is preventing the sensors from doing so?
One Pixel! 50x50 um
This limit is set by a operational amplifer (op amp) that lies inside the sensors circuit Every operational amplifier has a saturation voltage If an op amp has a saturation voltage of +/- 2 V a signal can look like this if it goes over.
To control the amount of voltage across the op amp one must adjust the capacitance as necessary Need capacitors with larger Capacitance
For 1 x-ray E=8keV E 3.6eV 2200 e h + Charge of electron q= 1.6*10-19 Q 2200 e 1.6 10 19 Q 0.35 fc
If you want to be below 2 volts (the usual op amp saturation) just use V= Q/C For a sensor that captures 3000 xrays/pixel/frame Q t 3000 0.35fC = 1.05 pc C = Q V & V 2 C 1.05pC 2V 525fF
The future sensors we wish to capture 50000 x- rays/pixel/frame Q t 50000 0.35fC = 17.5 pc C = Q V & V 2 C 17.5pC 2V 8.75pF
The X-ray (yellow blob) which contain s about 2200 Electrons or holes are captured in the sensor and force into the capacitor by switch From the capacitor the conversion from charge to voltage is made (V= Q/C)
Since there is not much space for large capacitors to go into the integrated circuit chip there had to be another way to get a larger capacitance out of a small amount of space This is done by nano-film capacitors!! With a small enough space taken up by the dielectric one could create a capacitor to meet the needs of the future sensors
The bottom metal conductor will be made of Titanium and Gold The dielectric will consist of Aluminum Oxide and Hafnium Oxide The top layer will be made of Aluminum
1) WBNONMETAL clean 2) WBDIFF clean 3) Grow 4000A thermal oxide 4) WBNONMETAL 5) Spin coat SPR3612 1.0 um 6) KS or EV 7) SVGDEV 8) Innotec Deposit Ti (50A) Au (200A) 9. Soak acetone overnight 10. Ultrasonic liftoff 11. Clean 12. ALD 100 A of AlO3, HfO2 13. Spin coat SPR3612 1.0 um 14. KS or EV 15. SVGDEV 16. Etch dielectric 17. Innotec 4000 A Aluminum
1) Spin coat SPR3612 1.0 um 2) KS or EV 3) SVGDEV 4) Aluminum etch at WBGENERAL 5) Clean
Apply image using KarlSuss and photo mask Evaporate 50 Å of Titanium and 200 Å of Gold with Innotec Liftoff Deposit hafnium oxide onto wafers using the Atomic Layer Deposition machine Fiji Apply second image using KarlSuss Etch Pad Evaporate 4000 Å of Aluminum Measure
After cleaning with different chemicals Apply photoresist, expose with mask, and develop
Evaporated 50 Å Titanium and 200 Å of Gold Then lift off!
Acetone
Bad Good
Due to time constraints I wasn t able to finish the last two layers. My hope is that future students will come to finish laying the dielectric and last metal down and compare my calculated capacitance with the actual. Never the less once finished the capacitors will be a great component to the LCLS sensors.
I would like to thank Astrid Tomada, Angelo Dragone, Jasmine Hasi and my mentor Christopher Kenney for helping me throughout this project. I would like to thank Steve Rock for all the help, and also my partner Shadey Edwards for working night shifts with me Thank you Department of Energy and SLAC for this wonderful opportunity