Introduction to MEMS Bruce K. Gale Overview Mechanical Engineering Department ! What is micromanufacturing and MEMS? BIOEN 6421, ELEN 5221, MEEN 5960 and 6960 ! Why the interest in MEMS? ! IC Fabrication Processes ! Bulk Micromachining Processes ! Surface Micromachining Processes ! Combined Processes ! References MEMS - evolved from the Microelectronics So what exactly is MEMS? Revolution Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and IC Industry Timeline electronics on a common substrate through the utilization of microfabrication technology or “microtechnology”. 1947 1958 1999 single transistor first IC 10 million transistors MEMS Timeline MEMS Examples 1980 pressure sensors 1999 accelerometers flow sensors inkjet printers Bulk micromachined pressure sensor deformable mirror devices gas sensors micromotors microgears lab-on-a-chip systems 2030 TI DMD ? (1.3 million micro-mirrors) The Opportunity of MEMS Technology General MEMS Advantages ! Batch fabrication – Reduced cost ! Reduced size – Is everything better smaller? ! Reduced power ! High precision ! New capabilities? ! Improved performance? The MicroTechnology/MEMS Tool Set Micromachining Processes ! Standard Integrated Circuit (IC) Processes Cleanroom plus microfab processes – Identical to those used in IC fabrication – Generally used for surface micromachining + ! Surface Micromachining – Additive processes ! Bulk Micromachining – Subractive Process ! Dividing line can become very blurry Standard IC Processes Standard IC Processes Source: Photolithography Jaeger Source: CWRU Source: Jaeger Standard IC Processes Standard IC Processes 1) Deposit/Grow Thin Films 2) Pattern Thin Films • Sputtering • Lithography • Evaporation • Etching Techniques (wet, dry, RIE) • Thermal Oxidation • CVD • Spinning • Epitaxy Standard IC Processes Micromachining Processes 3) Introduce Dopants (to form electrically-active Bulk Micromachining regions for diodes, transistors, etc.) • wet vs dry • isotropic vs anisotropic • Thermal Diffusion • subtractive process • Ion Implantation Micromachining Processes Micromachining Processes Bulk Micromachining Deep Reactive Ion Etching (DRIE) Source: Madou • high density ICP plasma • high aspect ratio Si structures • cost: $500K Source: LucasNova Source: Maluf Source: STS Source: STS Source: AMMI Source: Maluf MEMS Examples Micromachining Processes Pressure Sensor (conventional) Source: NovaSensor Wafer-Level Bonding • glass-Si anodic bonding • Si-Si fusion bonding • eutectic bonding • low temp glass bonding 60 50 40 30 20 Output Voltage Voltage (mV)Output 10 0 0 20406080100120 Source: UofL Source: Maluf Source: EV Pressure (PSI) Micromachining Processes Micromachining Processes Surface Micromachining LIGA (lithographie, galvanoformung, abformtechnik) • additive process • uses x-ray lithography (PMMA), electrodeposition and • structural & sacrificial layers molding to produce very high aspect ratio (>100) micro- structures up to 1000 um tall (1986) Source: Sandia Source: Madou Source: Kovacs MEMS Examples Micromachining Processes Micro-structures using LIGA Poor Man’s LIGA • uses optical epoxy negative-resist (SU-8) developed by IBM to produce high aspect ratio micro-structures (1995) UofL Micro-reaction wells: 150 um wide, 120 um tall, 50 um wall thickness Source: UW Source: Maluf MEMS Examples MEMS Examples Micromotors Optical MEMS (MOEMS) Source: MIT and Berkeley Source: NIST, Simon Fraser, UCLA, and MCNC MEMS Examples MEMS Examples Pressure Sensor (ultra-miniature) Lab-on-a-Chip Systems • separation • dilution • mixing and dispensing • analysis Source: NovaSensor Source: Caliper Integration EFFF Fabrication 1 ! Micromachining processes may be ! Anisotropic etching of Silicon integrated input and output ports in 20% KOH at 65 C with ! Both bulk and surface micromachining may Au Si N mask Conta Detect Ti be performed on a single substrate 3 4 ct or ! Deposit and pattern ! Micromachined structures may be Ti/Au electrodes on Silicon integrated with ICs front of wafer Polyimide ! Thick photosensitive polyimide or SU-8 used Silicon to define flow channels EFFF Fabrication 2 EFFF Fabrication 3 Output Port Input Port ! Remove Si N ! Completed channel 3 4 Silicon membrane looking from the top Channel Polyimide ! Deposit and pattern Glass Detector Electrode Channel Electrod Ti/Au electrode on glass Au substrate Ti ! Cross section through Glass channel showing ! Bond glass substrate to electrodes, polyimide Completed Cross Section polyimide using and substrates biocompatible UV Silicon curable adhesive Results- Results- Section Fabrication System Assembly Glass substrate with titanium, gold, and platinum electrode Silicon substrate with input/output ports, gold electrodes and patterned SU-8 Above- Complete device with input/output port connections Right- Complete systems with sample and buffer input, µ-EFFF system, and detectors MEMS Examples Fabrication Results Micromachined Tips for FEDs and AFMs ! Micrograph of detector wire Detection Wire across channel defined by polyimide ! Wire is 19 µm wide Output Port ! Location of wire Channel Sidewalls eliminates all end effects Source: Micron (?) Source: IBM MEMS Examples MEMS Examples Neural Probes Neural Interface Chip Source: Stanford Source: Mich (K. Wise) MEMS Examples MEMS Examples Micro-Grippers Micro-Tweezers Source: Berkeley Source: MEMS Precision Instruments MEMS Examples MEMS Examples Optical MEMS (MOEMS) Accelerometers Source: IMC (Sweden), Maluf and TI Sources: Analog Devices, Lucas NovaSensor, and EG&G IC Sensors MEMS Examples MEMS References Channels, Nozzles, Flow Structures, and Load Cells Fundamentals of Microfabrication; Marc J. Madou Micromachined Transducers Sourcebook; G. Kovacs An Introduction to MEMS Engineering; by Nadim Maluf Silicon Micromachining; by Elwenspoek and Jansen Microsensors; by Richard S. Muller, Roger T. Howe, Stephen D. Senturia, R. Smith (Editors) Micromechanics and Mems : Classic and Seminal Papers to 1990; by W. Trimmer (Editor) MEMS WWW Bookstore: http://mems.isi.edu/bookstore/ Source: EG&G IC Sensors.