Phillip Ahn Andrew Schnirel ENEE 416 October 9, 2007 The Concepts and Fundamentals of LIGA LIGA is a German term that stands for Lithography, Galvanoformung (meaning electroplating), and Abformung (meaning molding). LIGA uses a thick layer of photoresist as a mold, or well, to add high-aspect-ratios (the height is larger then the width) of metal onto a Silicon substrate in order to make a high precision micro sized devices. LIGA was invented by a team led by Erwin Becker and Wolfgang Ehrfeld working at the Institute for Nuclear Process Engineering at the Karlsruhe Nuclear Research Center in Germany in the early 1980’s [1]. The concepts of LIGA work in a very similar fashion to other semiconductor lithography steps. The process starts with a thin layer of metal deposited onto the wafer; this is called the seed layer or plating base. Next a thick layer of photoresist, usually PMMA (PolyMethyl MethAcrylate, commonly referred to as Plexiglas or acrylic glass) is deposited on the silicon wafer. After that a mask is placed over the wafer and the photoresist is exposed leaving the pattern that you want on the wafer. From there a thick layer of metal is deposited onto the holes on the wafer and the photoresist is stripped, leaving the thick layers of metal or possibly hard plastics behind. Steps in the LIGA process: The LIGA process has many distinct advantages over other manufacturing processes that set it apart from them. The process manufactures micro-scale pieces made typically made of metal, but can also be made out of plastic. Since LIGA uses lithography in its process it is allowed to make very smooth precise mechanical pieces with straight Electroforming step [3]. LIGA made Tensile Bar. All measurements in mm [4]. Substrate Preparation step [3]. Irradiation Step [3] Development step [3]. Resist Removal [3].sidewalls such as gears making it easier for production in assembly lines. Another advantage the LIGA has is the durability of the parts created. Some of the parts have been proven withstand up to 65,000 g’s [4]. One of the most common purposes of the LIGA process is MEMS. MEMS stands for MicroElectroMechanical Systems, and are special because at the size these machines are made the standard rules of classic Physics due not hold up. These devices are used in all aspects of technologies today. They can be found in optical switching, all different kinds of devices in cars (such as sensors and airbags), and Bio-Medical Engineering (such as implants and drug delivery devices). Some breaking edge technological groups are currently doing research into fast delivery fully mobile MEMS devices for the purpose of drug implants. Two of these devices being worked on at the Ceramics Processing Research Laboratory at the Massachusetts Institute of Technology are pictured on the right. Theses device being researched are for use by soldiers in the field of combat, but are currently being redesigned to better exploit the delivery system. Another important aspect of LIGA and MEMS is fiber optical applications. Fiber Optic Cables have become very important to technology and information transfer specifically. MEMS devices will make it easier to use this kind of technology. The picture to the right is of a T switch invented at Bell Labs in 1999. It uses a micro-mechanical switch to either allow the signal to go straight through or deflect it using a metal surface into a third, depending on weather the switch is up or down. This picture shows a line of 100 microns, just to give an idea of how small the mechanical switch and its parts actually are. MEMS technology has also become very prevalent in automobiles. Cars are using more and more MEMS for sensors for internal purposes. Some of the sensors that automobiles are currently using are airbag deployment sensors, pressure sensors, crash detectors, strain gauges, accerolometer measuring the acceleration, and a gyroscope for measuring the rotation of a tire. These systems are the beginning of more systems yet to come. As technology gets smaller and MEMS devices get more prominent these systems will be used more often throughout the car, especially into research of how the car is malfunctioning. Two MEMS devices [5]. Switch for Fiber Optical Cable [6]. Accelerometer [7]References [1] “LIGA” Wikipedia, September 8, 2007. October 5, 2007 <http://en.wikipedia.org/wiki/LIGA> [2] Jager, Richard C. Introduction To Microelectronic Fabrication Volume V Second Edition. New Jersey: Printice Hall, 2002. [3] “LiMiNT – LIGA Process” SSLS, October 5, 2007 <http://ssls.nus.edu.sg/facility/beamlines/limint/LIGA.htm> [4] “High Aspect Ratio Metal MEMS Technologies” AXSUN, April 10, 2003. October 6, 2007 <http://www.dtic.mil/ndia/2003fuze/rasmussen.pdf> [5] “Research at CPRL” Ceramics Processing Research Laboratory at MIT, February 15, 2007, October 7, 2007 < http://web.mit.edu/cprl/www/research.shtml> [6] “SeeSaw Switch is first practical MEMS optical switch” Bell Labs, February 23, 1999. October 7, 2007. <http://www.bell-labs.com/news/1999/february/23/1.html> [7] “Accelerometer” Wikipedia, October 4, 2007. October 7, 2007.