MEMS Sensors for Biomedical Applications Yu-Chong Tai Professor of EE Member of NSF/CNSE California Institute of Technology (NSF/ERC Industry Day, May 16-17, 2001) What is MEMS? A Micro-Electro-Mechanical System (MEMS) is a batch-fabricated (microfabricated) system that contains both electrical and mechanical components with characteristic sizes ranging from nanometers to millimeters Other Names • In US: Microdynamics • In Europe: Micro Systems (Technology) • In Japan: Micromachines, MicroRobots Machine Size Quantity Micromachines (MEMS) Conventional Machines Molecular (Nano) Machines nm µm mm m km Pressure Sensors 200 µm Nitride diaphragm Poly strain gauges Schlumberger Oil-Well Pressure Sensor nitride Diaphragms Polysilicon thermistor •10,000 ± psi design •Multi-diaphragm configuration output voltage (V) 0.65 0.6 0.55 0.5 0.45 1000 2000 3000 P ressu re (p si) 4000 5000 MEMS Pressure Sensor Probe for Intraocular Pressure Measurement Wafer with flexible pressure sensor skins Flexible ribbon Pressure sensor Sensor Tip Vacuum-Insulated Shear Stress Sensor Polysilicon Wire (3 x 150 x 0.5 µm3) Metal lead Polysilicon wire Vacuum Cavity (200 x 200 x µm3) Metal lead Nitride diaphragm Vacuum cavity Si substrate Cross-section Photograph Successful Test on NASAF 15 cm Shear-stress Sensor Imager Shear Stress (Pa) 2.86 cm M=0.9 Stanton Sensor M=0.7 M=0.5 M=0.3 Micro Sensor Time Multi-sensor chip: Pressure, Temperature and Flow mm 200 µm cm mm Shear stress sensor cm Five sensor clusters with a pitch of mm Pressure sensor Temperature sensor MEMS Mass Flow Meter N2 Channel chip Inlet Bonding wires Multi-sensor array chip picture of a packaged device PCB Schematic of packaged device Channel width: 2.5 mm Channel height: 0.2 mm Channel length: 18 mm P (mW) 6.5 6.0 5.5 5.0 0.0 0.5 1.0 Q1/2.2 1.5 Flow Rate Data 200 400 600 800 1000 1200 -0.001 Water Saline ∆ V [V] -0.002 -0.003 -0.004 -0.005 30 mA 36 mW -0.006 -0.007 Q [ul/min] Measures flow rates up to 10 µl/min Flow Sensor Transient Data 0.7590 Voltage [V] 0.7585 0.7580 0.7575 0.7570 0.7565 100 200 300 400 500 600 700 800 Time [sec] No Flow & Intermittent Power 900 Nanoflow (nl) Sensors Suspended Micro 200µm Channel Poly-Si Sensors Micro Channel 50 µm 100µm 100 µm 20 µm Nitride lightly B doped polysilicon heavily B doped polysilicon µm Si Cavity ~100 µm Temperature Change vs Flow Rate ∆T(oC) -1 Channel on substrate ST ≈ 0.0071oC/(nL/min) -2 -3 Suspended channel -4 ST ≈ 0.026 oC/(nL/min) Power ≈ 140µ µW Top ≈ 10 oC -5 100 200 Q (nL/min) 300 Sensor Resolution Histogram 14 12 Gausian Measurement Frequency 10 2σ 2σ 2.034 2.035 2.036 2.037 Sensor Output (V) Time-averaged Resolution ≈ nL/min 2.038 Monocyte Attachment through Molecular Recognition lipids trapped in arterial wall monocyte attachment flow lipids stimulate EC Endothelial cells (EC) Versatile Test Facility ow l F monocytes sec sec 2 Monocytes/Field Monocyte Attachment Control Ox-PAPC Ox-PAPC + Ox-PAPC + Ox-PAPC + High slew Rate Low Slew Rate Oscillating Flow ...What is MEMS? A Micro-Electro-Mechanical System (MEMS) is a batch-fabricated (microfabricated) system that contains both electrical... Micromachines, MicroRobots Machine Size Quantity Micromachines (MEMS) Conventional Machines Molecular (Nano) Machines nm µm mm m km Pressure Sensors 200 µm Nitride diaphragm Poly strain gauges Schlumberger... output voltage (V) 0.65 0.6 0.55 0.5 0.45 1000 2000 3000 P ressu re (p si) 4000 5000 MEMS Pressure Sensor Probe for Intraocular Pressure Measurement Wafer with flexible pressure sensor skins Flexible