05-11-2012, 01:14 PM
A SEMINAR REPORT ON MICRO ELECTRO MECHANICAL SYSTEMS (MEMS)
[attachment=38163]
ABSTRACT:
MEMS promises to revolutionize nearly every product category by bringing together silicon-based Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro-fabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes), the micromechanical components are fabricated using compatible "micromachining" processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
microelectronics with micromachining technology, making possible the realization of complete systems-on-a-chip. MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of microsensors and microactuators and expanding the space of possible designs and applications.
Microelectronic integrated circuits can be thought of as the "brains" of a system and MEMS augments this decision-making capability with "eyes" and "arms", to allow microsystems to sense and control the environment. Sensors gather information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The electronics then process the information derived from the sensors and through some decision making capability direct the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby controlling the environment for some desired outcome or purpose. Because MEMS devices are manufactured using batch fabrication techniques similar to those used for integrated circuits, unprecedented levels of functionality, reliability, and sophistication can be placed on a small silicon chip at a relatively low cost.
INTRODUCTION:
We're busy people. We tend to be somewhat macro-oriented….concerned with the big picture. And technology reflects this orientation. Our primary concerns are with the end result – what technology does for us on a day-to-day basis. We don't peel back the layers to see what makes technology work. And when you peel back those layers, it is inside the world of the miniature that some of the most exciting technology is taking place today -- where revolutionary advances allow new types of functionality to be incorporated onto the chipset. These advances have enabled the chip to think, act, and communicate -- in fact to become intelligent microsystems, or “systems-on-a-chip.”
Sand-sized machines:
The key enabling technology in this micro-domain is MEMS, or Micro-Electro-Mechanical Systems. MEMS are the microscopic structures integrated onto silicon that combine mechanical, optical and fluidic elements with electronics. Typically no bigger than a grain of sand, these MEMS devices are complex machines that enable chips to become intelligent. These devices act as the most direct links between digital electronics and the physical world, allowing the integration of electronics and mechanical systems on a single chipset.
25 years of history:
First developed in the 1970s and then commercialized in the 1990s, MEMS make it possible for systems of all kinds to be smaller, faster, more energy-efficient and less expensive. In a typical MEMS configuration, integrated circuits (ICs) provide the “thinking” part of the system, while MEMS complement this intelligence with active perception and control functions.
Sensing and acting:
MEMS are usually divided into two categories -- those devices that detect information, called microsensors, and those devices that can respond to information, or act, called actuators. Microsensors gather local information including, for example, thermal, biological, chemical, and optical input. The electronics of the devices can then process the information and may direct actuators to respond and control the environment (e.g. by moving, pumping, filtering) based on an intended, designed instruction.
MEMS Technology:
MEMS AND ICs: TWO OF A KIND
MEMS microstructures are manufactured in batch methodologies similar to computer microchips. The photolithographic techniques that mass-produce millions of complex microchips can also be used simultaneously to develop and produce mechanical sensors and actuators integrated with electronic circuitry. Most MEMS devices are built on wafers of silicon, adopting micromachining technologies from integrated circuit (IC) manufacturing and batch fabrication techniques.
Like ICs, the structures are developed in thin films of materials. The processes are based on depositing thin films of metal or crystalline material on a substrate, applying patterned masks by photolithographic imaging, and then etching the films to the mask. In effect, a sacrificial layer is introduced – a material which keeps other layers separated as the structure is being built up but is dissolved in the very last step allowing selective parts of the structure free to move.
MAKING THE TRANSITION: FROM PROTOTYPE TO MANUFACTURE
Prototyping is integral to the process, however. An initial device is produced that can be characterized, measured, and optimized for performance and high volume manufacture. A key challenge can be the leap from prototype to high volume manufacture – a transition that sometimes requires considerable modifications. This requires the availability of broad-based design and process expertise (not just application experience), as well as appropriate software tools that can automatically provide process customization. CAD tools are crucial to a cost and time-effective process. Previously developed internally, there are now several commercially available CAD packages that guide engineering teams through component design, system design, and analysis.
It's important to note that MEMS manufacturing technology is not a uniform science but rather a combination of design techniques and knowledge of materials, process, and applications. Processes may vary considerably. For example, the techniques used for wireless may not work at all for the development and production of optical communications devices. Further, although MEMS and IC manufacturing is based on photolithographic etching, in many cases the processes and/or materials may not be compatible. It's interesting to note that gold, which is required in the manufacture of optical MEMS, will contaminate an IC batch.
MICROELECTROMECHANICAL SYSTEMS DESCRIPTION:
MEMS technology can be implemented using a number of different materials and manufacturing techniques; the choice of which will depend on the device being created and the market sector in which it has to operate.
Silicon:
Silicon is the material used to create most integrated circuits used in consumer electronics in the modern world. The economies of scale, ready availability of cheap high-quality materials and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking. The basic techniques for producing all silicon based MEMS devices are deposition of material layers, patterning of these layers by photolithography and then etching to produce the required shapes.
MEMS Components:
The miniaturization, multiplicity, and microelectronics characteristics of MEMS technology make it especially attractive to realize small-size, low-cost, high-performance systems integrated on one chip. Microfabricated pressure sensors have dominated the MEMS application market for the last two decades. With advances in IC technology and corresponding progress in MEMS fabrication processes in the last decade, additional integrated microsensor and microactuator systems are now being commercialized, and even more applications are expected to benefit. In this section, we present examples of some commercially available MEMS components selected on the basis of fabrication technique and system complexity. First, pressure sensors are presented as an example of a MEMS device fabricated using bulk micromachining, followed by integrated accelerometers that are fabricated by surface micromachining. Next, the suitability of MEMS technology in complex, array-type application systems is demonstrated using the example of a digital micromirror device (DMD). Finally, the potential of MEMS components in aerospace applications is discussed, and some promising devices are listed.
MEMS SENSORS:
Pressure Sensors
MEMS technology has been utilized to realize a wide variety of differential, gauge, and absolute pressure microsensors based on different transduction principles. Typically, the sensing element consists of a flexible diaphragm that deforms due to a pressure differential across it. The extent of the diaphragm deformation is converted to a representative electrical signal, which appears at the sensor output.
Figure 1.10 shows a manifold absolute pressure (MAP) sensor for automotive engine control, designed to sense absolute air pressure within the intake manifold (manufactured by Motorola, Schaumburg, Illinois). This measurement can be used to compute the amount of fuel required for each cylinder in the engine. The microfabricated sensor integrates on-chip, bipolar op-amp circuitry and thin-film resistor networks to provide a high output signal and temperature compensation.
[attachment=38163]
ABSTRACT:
MEMS promises to revolutionize nearly every product category by bringing together silicon-based Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro-fabrication technology. While the electronics are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes), the micromechanical components are fabricated using compatible "micromachining" processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
microelectronics with micromachining technology, making possible the realization of complete systems-on-a-chip. MEMS is an enabling technology allowing the development of smart products, augmenting the computational ability of microelectronics with the perception and control capabilities of microsensors and microactuators and expanding the space of possible designs and applications.
Microelectronic integrated circuits can be thought of as the "brains" of a system and MEMS augments this decision-making capability with "eyes" and "arms", to allow microsystems to sense and control the environment. Sensors gather information from the environment through measuring mechanical, thermal, biological, chemical, optical, and magnetic phenomena. The electronics then process the information derived from the sensors and through some decision making capability direct the actuators to respond by moving, positioning, regulating, pumping, and filtering, thereby controlling the environment for some desired outcome or purpose. Because MEMS devices are manufactured using batch fabrication techniques similar to those used for integrated circuits, unprecedented levels of functionality, reliability, and sophistication can be placed on a small silicon chip at a relatively low cost.
INTRODUCTION:
We're busy people. We tend to be somewhat macro-oriented….concerned with the big picture. And technology reflects this orientation. Our primary concerns are with the end result – what technology does for us on a day-to-day basis. We don't peel back the layers to see what makes technology work. And when you peel back those layers, it is inside the world of the miniature that some of the most exciting technology is taking place today -- where revolutionary advances allow new types of functionality to be incorporated onto the chipset. These advances have enabled the chip to think, act, and communicate -- in fact to become intelligent microsystems, or “systems-on-a-chip.”
Sand-sized machines:
The key enabling technology in this micro-domain is MEMS, or Micro-Electro-Mechanical Systems. MEMS are the microscopic structures integrated onto silicon that combine mechanical, optical and fluidic elements with electronics. Typically no bigger than a grain of sand, these MEMS devices are complex machines that enable chips to become intelligent. These devices act as the most direct links between digital electronics and the physical world, allowing the integration of electronics and mechanical systems on a single chipset.
25 years of history:
First developed in the 1970s and then commercialized in the 1990s, MEMS make it possible for systems of all kinds to be smaller, faster, more energy-efficient and less expensive. In a typical MEMS configuration, integrated circuits (ICs) provide the “thinking” part of the system, while MEMS complement this intelligence with active perception and control functions.
Sensing and acting:
MEMS are usually divided into two categories -- those devices that detect information, called microsensors, and those devices that can respond to information, or act, called actuators. Microsensors gather local information including, for example, thermal, biological, chemical, and optical input. The electronics of the devices can then process the information and may direct actuators to respond and control the environment (e.g. by moving, pumping, filtering) based on an intended, designed instruction.
MEMS Technology:
MEMS AND ICs: TWO OF A KIND
MEMS microstructures are manufactured in batch methodologies similar to computer microchips. The photolithographic techniques that mass-produce millions of complex microchips can also be used simultaneously to develop and produce mechanical sensors and actuators integrated with electronic circuitry. Most MEMS devices are built on wafers of silicon, adopting micromachining technologies from integrated circuit (IC) manufacturing and batch fabrication techniques.
Like ICs, the structures are developed in thin films of materials. The processes are based on depositing thin films of metal or crystalline material on a substrate, applying patterned masks by photolithographic imaging, and then etching the films to the mask. In effect, a sacrificial layer is introduced – a material which keeps other layers separated as the structure is being built up but is dissolved in the very last step allowing selective parts of the structure free to move.
MAKING THE TRANSITION: FROM PROTOTYPE TO MANUFACTURE
Prototyping is integral to the process, however. An initial device is produced that can be characterized, measured, and optimized for performance and high volume manufacture. A key challenge can be the leap from prototype to high volume manufacture – a transition that sometimes requires considerable modifications. This requires the availability of broad-based design and process expertise (not just application experience), as well as appropriate software tools that can automatically provide process customization. CAD tools are crucial to a cost and time-effective process. Previously developed internally, there are now several commercially available CAD packages that guide engineering teams through component design, system design, and analysis.
It's important to note that MEMS manufacturing technology is not a uniform science but rather a combination of design techniques and knowledge of materials, process, and applications. Processes may vary considerably. For example, the techniques used for wireless may not work at all for the development and production of optical communications devices. Further, although MEMS and IC manufacturing is based on photolithographic etching, in many cases the processes and/or materials may not be compatible. It's interesting to note that gold, which is required in the manufacture of optical MEMS, will contaminate an IC batch.
MICROELECTROMECHANICAL SYSTEMS DESCRIPTION:
MEMS technology can be implemented using a number of different materials and manufacturing techniques; the choice of which will depend on the device being created and the market sector in which it has to operate.
Silicon:
Silicon is the material used to create most integrated circuits used in consumer electronics in the modern world. The economies of scale, ready availability of cheap high-quality materials and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking. The basic techniques for producing all silicon based MEMS devices are deposition of material layers, patterning of these layers by photolithography and then etching to produce the required shapes.
MEMS Components:
The miniaturization, multiplicity, and microelectronics characteristics of MEMS technology make it especially attractive to realize small-size, low-cost, high-performance systems integrated on one chip. Microfabricated pressure sensors have dominated the MEMS application market for the last two decades. With advances in IC technology and corresponding progress in MEMS fabrication processes in the last decade, additional integrated microsensor and microactuator systems are now being commercialized, and even more applications are expected to benefit. In this section, we present examples of some commercially available MEMS components selected on the basis of fabrication technique and system complexity. First, pressure sensors are presented as an example of a MEMS device fabricated using bulk micromachining, followed by integrated accelerometers that are fabricated by surface micromachining. Next, the suitability of MEMS technology in complex, array-type application systems is demonstrated using the example of a digital micromirror device (DMD). Finally, the potential of MEMS components in aerospace applications is discussed, and some promising devices are listed.
MEMS SENSORS:
Pressure Sensors
MEMS technology has been utilized to realize a wide variety of differential, gauge, and absolute pressure microsensors based on different transduction principles. Typically, the sensing element consists of a flexible diaphragm that deforms due to a pressure differential across it. The extent of the diaphragm deformation is converted to a representative electrical signal, which appears at the sensor output.
Figure 1.10 shows a manifold absolute pressure (MAP) sensor for automotive engine control, designed to sense absolute air pressure within the intake manifold (manufactured by Motorola, Schaumburg, Illinois). This measurement can be used to compute the amount of fuel required for each cylinder in the engine. The microfabricated sensor integrates on-chip, bipolar op-amp circuitry and thin-film resistor networks to provide a high output signal and temperature compensation.