MEMS Endovascular Pressure Sensors

1. MEMS Endovascular Pressure Sensors Jonathan Brickey, Niels Black, Charles Wang December 14, 2007

2. Vena Cava Right Atrium Right Ventricle Pulmonary Arteries Lungs Pulmonary Veins Left Atrium Left Ventricle Aorta Body Anatomy of the Heart http://www.nhlbi.nih.gov/health/dci/Diseases/pda/pda_heartworks.html

3. 2 cm 6 cm Abdominal Aorta Aneurysm Healthy Blood Pressure Diastole: <80 mmHg (11 kPa) Systole: <120 mmHg (16 kPa) Hypertension Stage 2 Diastole: >100 mmHg (13 kPa) Systole: >160 mmHg (21 kPa) http://www.ultrasoundspecialists.com/screenings.html

4. Prevalence of AAA • 10th leading cause of death – 65-74 years old • 5-7% men over 60 diagnosed with AAA • 1-3% men over 65 experience aortic rupture • 75-90% mortality rate from rupture • 11:1 male:female ratio – 60-64 years old

5. Endovascular Repair Open Repair Methods of Treatment http://www.nhlbi.nih.gov/health/dci/Diseases/arm/arm_treatments.html http://www.vascularweb.org/_CONTRIBUTION_PAGES/Patient_Information/NorthPoint/Abdominal_Aortic_Aneurysm.html

6. EndoSure by CardioMEMS • EndoSure Wireless AAA Pressure Measurement System • Permanently implanted • Radio frequency transmission • Radio frequency powered • Size of a paper clip • Biocompatible http://www.physorg.com/news10533.html http://www.cardiomems.com/content.asp?display=medical+mb&expand=ess

7. Jay S. Yadav, M.D and Mark G. Allen 1995 – cofound CardioMEMS 2005 – EndoSure sensor invented April, 2007 – granted FDA approval Design Record http://www.physorg.com/news10533.html

8. 1967 C. C. Collins“Miniature Passive Pressure Transensor for Implanting in the Eye “

9. 1992 Lars Rosengren 1995, William N.Carr, NJIT Hartley Oscillator

10. 1999-2002 Mark Allen, GA Tech Wireless micromachined ceramic pressure sensors High temperature self packaged wireless ceramic pressure sensor

11. Flexible Wireless Passive Pressure Sensors for Biomedical Applications 2006 – Mark Allen, GA Tech

12. Flexible Substrates: Types • Liquid Crystal Polymers (LCP) • Almost as ordered as fully crystalline solids • Chemically inert • Easy to fabricate • Polyamide Films • Kapton-E (DuPont) • thermal expansion coefficient same as Cu • 13-50 micron thickness

13. Flexible Substrates: Advantages • For machining application: • Very high dimensional stability • High etchability – heavily isotropic • For biomedical applications: • Flexibility allows less invasive implantation • High levels of chemical inertness

14. MEMS Screenprinting • Additive process: • Mesh overlay – polyester or steel • Places where material does not go are “painted” over • Mesh screen placed on substrate, liquid poured over

15. MEMS Screenprinting Advantages/Disadvantages: • Cheap! • Does not require pressurization or extremely expensive equipment, like lithography • Mesh can be reused • Not particularly precise • Features can be no smaller than mesh spacing (~50 µm)

16. Lithography Lithography mask for Inductor-Capacitor setup Cross-section of Cu application (Fonseca 2006)

17. Capacitance vs. Pressure

18. Power and Signal Transmission

19. Final Output

20. Problems in Simplification • Actual capacitor shape not circular: • “…tapered in the center to reduce deflection and avoid shorting out the capacitor…” (Fonseca 2006) • Circular model shorts out just before 13 kPa • Inductance • Very simplified: • Most MEMS inductors use complicated programs

21. Future Improvements • Major limitations: Size, Sensitivity, Transmission Distance • MEMS fabrication results in increased sensitivity • Size and Transmission Distance invariably linked

22. Other Possible Design Improvements • Finite element analysis of coil design inductance • Substrates with low dielectric constants • Hartley oscillators or other more complex CMOS for improving sensitivity or transmission distance

23. References • Wiemer, M., Frömel, J., Jia, C., Geßner, T., “Bonding and contacting of MEMS-structures on wafer level.” The Electrochemical Society - 203rd meeting, Paris (France), 2003 April 27- May 2 • Fonseca, M.A.; English, J.M.; von Arx, M.; and Allen, M.G., "Wireless Micromachined Ceramic Pressure Sensor for High Temperature Applications," IEEE J. Microelectromechanical Systems, vol. 11, no.4, p. 337-43 (2002) • Fonseca, M.A., Kroh, J., White, J., and Allen, M.G., “Flexible Wireless Passive Pressure Sensors for Biomedical Applications,” Tech. Dig. Solid-State Sensor, Actuator, and Microsystems Workshop (Hilton Head 2006), June 2006

24. References (continued) • “New Medical Device Combines Wireless and MEMS Technology,” Physorg.com, February 03, 2006, December 08, 2007, <http://www.physorg.com/news10533.html> • Rosengren, L., Backlund, Y., Sjostrom, T., Hok, E., and Svedbergh, B., “A System for Wireless Intra-Ocular Pressure Measurements Using a Silicon Micromachined Sensor,” (1992) • Collins, C.C., “Miniature Passive Pressure Transensor for Implanting in the Eye,” IEEE Transactions on Biomedical Engineering, vol. BME-14, no. 2, April, 1967 • Allen, M.G., “Implantable micromachined wireless pressure sensors: approach and clinical demonstration,” 2nd International Workshop on BSN 2005 Wearable and Implantable Body Sensor Networks, 2005, p 40-1.