Micro-electro Mechanical Systems
Published on Dec 12, 2015
The satellite industry could experience its biggest revolution since it joined the ranks of commerce, thanks to some of the smallest machines in existence. Researchers are performing experiments designed to convince the aerospace industry that microelectromechanical systems (MEMS) could open the door to low-cost, high-reliability, mass-produced satellites.
MEMS combine conventional semiconductor electronics with beams, gears, levers, switches, accelerometers, diaphragms, microfluidic thrusters, and heat controllers, all of them microscopic in size.
"We can do a whole new array of things with MEMS that cannot be done any other way," said Henry Helvajian, a senior scientist with Aerospace Corp., a nonprofit aerospace research and development organization in El Segundo, Calif.
Microelectromechanical Systems, or MEMS, are integrated micro devices or systems combining electrical and mechanical components. They are fabricated using integrated circuit (IC) batch processing techniques and can range in size from micrometers to millimeters. These systems can sense, control and actuate on the micro scale, and function individually or in arrays to generate effects on the macro scale.
MEMS is an enabling technology and current applications include accelerometers, pressure, chemical and flow sensors, micro-optics, optical scanners, and fluid pumps. Generally a satellite consists of battery, internal state sensors, communication systems and control units. All these can be made of MEMS so that size and cost can be considerably reduced. Also small satellites can be constructed by stacking wafers covered with MEMS and electronics components. These satellites are called 'I' Kg class satellites or Picosats. These satellites having high resistance to radiation and vibration compared to conventional devices can be mass-produced there by reducing the cost.
These can be used for various space applications.Also small satellites can be constructed by stacking wafers covered with MEMS and electronics components. These satellites are called 'I' Kg
Although MEMS devices are extremely small MEMS technology is not about size. Instead, MEMS is a manufacturing technology; a new way of making complex electromechanical systems using batch fabrication techniques similar to the way integrated circuits are made and making these electromechanical elements along with electronics.
The material used for manufacturing MEMS is Silicon. Silicon possesses excellent materials properties making it an attractive choice for many high-performance mechanical applications (e.g. the strength-to-weight ratio for silicon is higher than many other engineering materials allowing very high bandwidth mechanical devices to be realized).
COMPONENTS OF MEMS
Micro-Electro-Mechanical Systems (MEMS) is the integration of mechanical elements, sensors, actuators, and electronics on a common silicon substrate through the utilization of micro fabrication technology. MEMS is truly an enabling technology allowing the development of smart products by augmenting the computational ability of microelectronics with he perception and control capabilities of micro sensors and micro actuators.
Microelectronic integrated circuits (ICs) can be thought of as the "brains" of systems and MEMS augments this decision-making capability with "eyes" and "arms", to allow micro systems to sense and control the environment.
MEMS are usually divided into two categories -- those devices that detect information, called micro sensors, and those devices that can respond to information, or act, called actuators. Micro sensors 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 FABRICATION PROCESSES (Basic Concepts)
The electronics parts are fabricated using integrated circuit (IC) process sequences (e.g., CMOS, Bipolar, or BICMOS processes) and the micro mechanical components are fabricated using compatible "micro machining" processes that selectively etch away parts of the silicon wafer or add new structural layers to form the mechanical and electromechanical devices.
The design process of MEMS starts with the fabricator, who gives the original concept of the device to the designer, i.e. it specifies the layout rules and other required details for the process. The designer will then translate the requirements into circuit design, i.e. the components that are required, their values and the manner in which they must be interconnected is decided.
In fabricating a specific circuit or a class of circuits a set of patterns are sequentially transferred onto silicon. Each pattern is called a mask and could represent either a pattern of desired impurity to be introduced into the silicon wafer or layer to be deposited on to, grown on, or removed from the wafer. Thus there is associated with each pattern transfer a lithographic step, and a set’ of unit pr6cesses which perform the desired task of introducing the impurity in to or depositing on the wafer.
The technological step carried out for lithography, i.e. diffusion chemical vapor deposition or etching, determines whether material introduction, deposition or removal is done. The process sequence usually requires several masks and that a single silicon wafer is designed to contain several repeated patterns. During wafer processing several wafers are processed simultaneously, i.e they are batch processed.
Each batch of wafers is called a lot. Each wafer consists of hundreds of identical circuits called die, which is separated from each other by silicon paths called scribe tracks, which is chosen along cleavage planes of silicon. The dice are separated and individual chips are obtained. Subsequently, chip assembly takes * place, where the chips are mounted on headers external leads are connected and sealed.
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