MICRO ELECTRO MECHANICAL SYSTEM - MEMS

MICRO ELECTRO MECHANICAL SYSTEM

                                            Microelectromechanical systems (MEMS, also written as micro-electro-mechanical, Microelectromechanical or microelectronic and microelectromechanical systems and the related micro mechatronics) is the technology of microscopic devices, particularly those with moving parts. It merges at the Nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micro machines in Japan, or micro systems technology (MST) in Europe.

              

                                  MEMS technology consist of microelectronic elements actuators, sensors and mechanical structures built onto a substrate which is usually “Silicon”. They are developed using micro fabrication techniques: deposition, patterning, etching. Micro-Electro-Mechanical Systems, or MEMS, is a technology that in its most general form can be defined as miniaturized mechanical and electromechanical elements that are made using the techniques of micro fabrication. The critical physical dimensions of MEMS devices can vary from well below one micron on the lower end of the dimensional spectrum, all the way to several millimeters. Likewise, the types of MEMS devices can vary from relatively simple structures having no moving elements, to extremely complex electromechanical systems with multiple moving elements under the control of integrated microelectronics. The one main criterion of MEMS is that there are at least some elements having some sort of mechanical functionality whether or not these elements can move. The term used to define MEMS varies in different parts of the world. In the United States they are predominantly called MEMS; while in some other parts of the world they are called “Microsystems Technology” or “micro machined devices”. micro sensors and microactuatorare appropriately categorized as “transducers”, which are defined as devices that convert energy from one form to another. In the case of micro sensors, the device typically converts a measured mechanical signal into an electrical signal.

COMPONENT OF MEMS

1. Microelectronics

The microelectronics of a MEMS are very similar to chips as we think of them today. The microelectronics act as the "brain" of the system. It receives data, processes it, and makes decisions. The data received comes from the micro sensors in the MEMS.

2. Micro Sensors

 The micro sensors act as the arms, eyes, nose, etc. They constantly gather data from the surrounding environment and pass this information on to the microelectronics for processing. These sensors can monitor mechanical, thermal, biological, chemical, optical and magnetic readings from the surrounding environment.

3. Micro Actuators

A micro actuator acts as a switch or a trigger to activate an external device. As the microelectronics is processing the data received from the micro sensors, it is making decisions on what to do based on this data. Sometimes the decision will

involve activatin3g an external device. If this decision is reached, the microelectronics will tell the micro actuator to activate this device.

4. Microstructures

 Due to the increase in technology for micromachining, extremely small structures can be built onto the surface of a chip. These tiny structures are called micro structures and are actually built right into the silicon of the MEMS. Among other things, these microstructures can be used as valves to control the flow of a substance or as very small filters.

MEMS Manufacturing Technologies

There are three types of technologies for manufacturing "MEMS" which are as follows:

1. Bulk Micromachining

2. Surface Micromachining

3. High Aspect Ratio (HAR) Silicon Micromachining

High Aspect Ratio (HAR) Silicon Micromachining

                                         Both bulk and surface silicon micromachining are used in the industrial production of sensors, ink-jet nozzles, and other devices. But in many cases the distinction between these two has diminished. A new etching technology, deep reactive-ion etching, has made it possible to combine good performance typical of bulk micromachining with comb structures and in-plane operation typical of surface micromachining. While it is common in surface micromachining to have structural layer thickness in the range of 2 μm, in HAR silicon micromachining the thickness can be from 10 to 100 μm. The materials commonly used in HAR silicon micromachining are thick polycrystalline silicon, known as epi-poly, and

bonded silicon-on-insulator (SOI) wafers although processes for bulk silicon wafer also has been created (SCREAM). Bonding a second wafer by glass frit bonding, anodic bonding or alloy bonding is used to protect the MEMS structures. Integrated circuits are typically not combined with HAR silicon micromachining.

BENEFITS OF MEMS

1. Much smaller area

2. Cheaper than alternatives

3.  In medical market, that means disposable

4.  Can be integrated with electronics (system on one chip)

5.  Speed:

6.  Lower thermal time constant

7.  Rapid response times (high frequency)

8.  Power consumption:

9.  low actuation energy

10. low heating power

11. Imperfect fabrication techniques

12.  Difficult to design on micro scales