Introduction

Enhanced Geothermal Systems • Enhanced Geothermal Systems (EGS) is an energy technology that

harnesses the heat of the earth. Impermeable rock kilometers below the surface of the earth is fractured creating a network of fractures through which water may flow. Water is pumped down into the system of fractures where it picks up the earth’s heat. It then returns to the surface of the earth where the heat is converted to electrical energy.

• EGS is a renewable and steady source of Energy with very low emissions.

• An MIT study estimates the amount of extractable heat in the US to “exceed 200,000 EJ or about 2,000 times the annual consumption of primary energy in the United States in 2005.” [1]

• EGS energy production would benefit from improvements in well monitoring technology

Project Overview

In order for new sensors to safely be tested in the lab a geothermal environment must be simulated using a pressure vessel. The aim of this project is to develop a pressure vessel for the safe testing of MEMS sensor robustness and functionality in a geothermal environment.

Parameters

Must operate safely at up to 30 MPa of pressure and temperatures of up to 400°C The inside of the vessel must be made of or coated with chemically inert materials that will not react with the geothermal

brine The chip needs to be stabilized within the vessel Any wiring (including wire-bonding on the circumferential area of the surface of the MEMS chip) must be isolated from the

geothermal brine The design must include safeguards from bursting and/or leaking Incorporate an electrical feed-through in the vessel wall for maintaining communication with the chip during testing Incorporate a feed-through for pressure control

Harsh Environment MEMS Sensors • A Microelctromechanical systems (MEMS) chip is a micro scale device that

combines electrical and mechanical physics to make sensors and actuators

• Harsh Environment MEMS sensors currently in development at UC Berkeley will be used for down-hole monitoring of Enhanced Geothermal Systems to sense things such as temperature, pressure, and pH. Materials being explored for use in the fabrication of harsh environment MEMS chips include silicon carbide, sapphire, and synthetic diamond. These materials can withstand high temperature and pressure, and resist corrosion when in contact with corrosive media.

Pressure Vessel Design for the Testing of MEMS Sensors in a Geothermal Environment Chuck Cusumano Sarah Wodin-Schwartz Professor Albert Pisano

Pencil-and-Paper Sketches

Solidworks (Auto-CAD) Future Work

Acknowledgements Sources [1] Massachusetts Institute of Technology, “Future of Geothermal Energy: Impact of Enhanced Geothermal Systems (EGS) on the

United States in the 21st Century,” (2006) [2] U.S. Dept. of Energy. An Evaluation of Enhanced Geothermal Systems Technology. 2008 [3] http://www.epn-online.com/page/new56023/phase-iv-engineering-unveils-new-passive-rfid-chip.html [4] http://www.cmr.wsu.edu/cleanroom/applications/mems_packaging [5] SEM image by Sarah Wodin-Schwartz [6] Jaeger, Richard C. Introduction to Microelectronic Fabrication. Upper Saddle River, N.J: Prentice Hall, 2002. Print. (193)

Chuck would like to thank Professor Pisano for allowing him to be an intern in his lab and for his advice and expertise. Chuck also gives a special thanks to Sarah Wodin-Schwartz for making his internship possible and for her daily consultation, guidance and encouragement. Finally, thanks to all the grad students in the BMAD lab for sharing their work space and for their support.

(above) Pros: axial loading, easy assembly Cons: Screws exposed to geothermal environment, wires are etched through center of chip (above) Pros: axial loading, wire bonding

Cons: complex thrust bearing assembly, there is a problem with the seal, difficult to fabricate, large

(left and right)Pros: axial loading, wire bonding, simple design Cons: custom built package, difficult to fabricate and assemble, large

• safety analyses of current model

• fabrication of current model • explore other design ideas

that may be easier to fabricate and assemble (see below)

• explore idea of using disposable packaging for chip testing

custom two-piece package routes wires through bottom o-ring

gold o-ring

Au-Sn Preform

MEMS chip (10mmx10mm)

spacer shim

cap will be held tightly together with nuts and bolts (not shown)

[2]

[3]

[4]

[6]

[5]

seal formed by pressure between cap, o-ring, and chip

nuts and bolts will clamp top and bottom cap pieces, compressing rubber safety gasket (not shown) and engaging the seal

Here the cap is inserted into cylindrical pressure vessel, on the other end a cap is screwed over the vessel body

feed-through welded into cap body