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|   Manufacturing Processes   |
Waddan’s manufacturing processes are derived from semiconductor processing. Most of the manufacturing equipment and tools used by the semiconductor industry are adopted for sensor manufacturing. The examples of manufacturing processes are as follows:

Bulk Micromachining

BMM_IntroJust as a machinist uses machine tools like lathe, borer, or shaper to remove material from a block of metal to produce a desired part, a bulk micromachinist does the same at micro level, only his tools involves photo processing and chemical etching and some tricks of the .trade routinely performed in semiconductor industry. A variety of materials are employed for such micromachining, but silicon is predominantly used because it is well understood, it is cheaper than other materials in the processing category, and most importantly the equipment used in semiconductor industry can be readily customized for this purpose. Finally, when supporting electronics is necessary, it can be built around the machined part. In addition to silicon, alumina, sapphire, Pyrex, quartz, GaAs, Lithium Niobate, Lithium Tantalate etc. are also employed for sensor manufacturing. With careful design and processing plans practically any shape imagined can be formed by bulk micromachining. Nevertheless, to date silicon has the best processing time and cost advantage over the other materials. The bulk micromachined devices are usually encapsulated by glass or some other substrate. Therefore, the devices generally have three substrates. The typical thicknesses involved are shown in the figure.

Surface Micromachining

SMM_IntroSurface micromachining is the fabrication of micromechanical structures by deposition and etching of thick structural and sacrificial films. Thus, simple microstructures like beams or membranes as well as complex structures like serpentine springs, gimbals, resonators, switches can be fabricated on top of a silicon substrate. The main features of the surface micromachining technology are the small microstructure dimensions and the opportunity to integrate micromechanics and microelectronics on the same chip. By use of VLSI compatible batch processing, low cost microstructure fabrication can be achieved for high volume applications. However, the thermal warping or distortion of the sensing element and the flexures involved is a common problem as the operating temperature varies. Operation at nominally fixed temperature is necessary for predictable responses.


MM_IntroMicromolding is a process of making electrodeposited castings in molds made in photosensitive sacrificial materials like PMM resists using optical imaging. Generally, the casts are 2D structure, but sometimes 3D structures are also made using a multi-step micromolding technique. The deposition materials chosen are usually nickel, gold or copper. The molding cavities are made on a silicon substrate with a Ti film using photolithography. After completing the deposition, the resist is dissolved leaving the sensing element along with the surrounding support structures. To complete the device fabrication, the micromolded elements are transfer bonded to a Pyrex glass wafer, and the wafer used during deposition is removed by removing the Ti film.

Laser Machining

LMM_IntroLaser machining is used mostly for cutting to release sensing elements which otherwise would break off during wafer processing. In its low power form, the laser is also used to make positive ohmic contact (welding of two metallic film surfaces bearing against each other). At microscopic level, a laser cut line is not as smooth as that made by etching along crystal planes. That's why it is difficult to form a complete micro device using laser machining alone. It is mostly used as an assisting technology to trim parts of structure that is difficult to form using standard methods.