Batch fabrication

Even the tight controls in siUcon integrated circuit manufacturing are not yet sufficient to produce absolutely identical sensors on a single wafer. Cahbration of the final product is usually necessary, often by adjusting the value of a circuit element on the IC such as a resistor. The caUbration process can be automated, but it stiU adds to the cost of batch-fabricated sensors. Clever means of self-caUbration, particularly in field use, are constantiy being sought. 

A prerequisite for all etch-stop techniques discussed so far is an electrical connection to an external power supply. However, if the potential required for passivation in alkaline solutions is below 1 V, it can be generated by an internal galvanic cell, for example by a gold-silicon element [As4, Xil]. An internal galvanic cell can also be realized by a p-n junction illuminated in the etchant, as discussed in the next section. Internal cells eliminate the need for external contacts and make this technique suitable for simple batch fabrication. 

Silicon devices can be batch-fabricated using the technology currently used for fabricating integrated circuits. 

L. M. Roylance and J. B. Angell, A batch-fabricated silicon accelerometer, IEEE Trans. Electron Devices 26(12), 1911, 1979. 

In this section we therefore introduce the special challenges of automotive sensor testing. First, some specific characteristics of sensing devices with respect to testability for functional parameters are pointed out. Then, conclusions are deduced leading to an optimized approach to test methods suitable for batch fabrication processes (i.e., model-based tests, test functions, test-pattern based tests, parameter extraction methods based on on-wafer tests). Practical examples show the potential of the methodical approach. 

Identify functionally critical model parameters for which the tolerance bands of available batch fabrication processes do not comply with those calculated above. Consider alternative processing technologies and redesign the sensor so that the number of critical parameters is minimized (see Section 4.1). 

Another variation on solution casting is spin coating. This technique borrows from the methods developed by the semiconductor industry to deposit very thin and uniform layers of photoresist onto silicon wafers. This method has been successfully used in the sensor industry to deposit polymer electrolyte membranes onto silicon-based gas sensors [21]. Some main advantages of spin coating are that very thin and reproducible films can be produced, and that an entire array of sensors can be coated simultaneously using batch fabrication methods. In addition, spin coating equipment is readily available fi"om the semiconductor industry. 

Goldberg, H. D., Brown, R. B., Lin, D. R and Meyerhoff, M. E. (1994) Screen printing a technology for the batch fabrication of integrated chemical-sensor arrays. Sensors and Actuators B Chemical 21,171-83. 

In view with microelectrode arrays F. Blair Simmons in 1965 performed the first multichannel auditory prosthesis stimulation study with five stainless steel electrodes insulated with Formvar inserted into the auditory nerve (and not into the ST) and emerging out from cochlea [27]. In recent years the interest in alternative stiff electrodes, to be inserted directly into the auditory nerve, has revived. In research conducted at University of Michigan, a batch-fabricated cochlear electrode array with stacked layers of parylene and metal was fabricated by silicon micromachining techniques. The 32-site array contained IrO (Iridium Oxide) stimulation sites with a centre-to-centre site spacing of 250 pm [28]. In the following sections the stiff and flexible electrode designs from the Delft University of the Technology (TU Delft), The Netherlands are described with its micro-fabrication sequence done at The Delft Institute of Microsystems and Nanoelectronics (DIMES), TU Delft, The Netherlands. 

A major research thrust in microfluidic science and technology is the development of autonomous platforms for the extraction and purification of biological material from cells. Batch fabricated diagnostic and medical treatment units hold great potential to enable both research and healthcare advances. This article presents research focused on sample extraction and purification with an emphasis on steps taken toward miniaturizing one of the fundamental preparative techniques used in molecular biology DNA extraction and purification from a complex biological sample. After the extraction... 

Top-down nanochannel fabrication techniques are developed mainly over the last decade with state-of-the-art micromachining facilities. Various kinds of nanochannels, such as short nanopores, 2D nanoslits, and ID nanotubes, have been fabricated and tested for different applications. Small nanopores are made based on the reflow of surface atoms under the irradiation of focused ion or electron beams. 2D nanoslits can be easily batch fabricated with either etching of enclosed sacrificial lines or bonding of two chips with one having etched nanometer deep open channels on it. ID nanochannels need advanced lithography capability, and many techniques are not suitable for batch fabrication. Some more details of making these three types of nanochannels are as follows. 

Fabrication of 2D Nanochannels Fabrication of 2D nanochannels can be easily done with state-of-the-art microfabrication facilities based on either sacrificial lines or bonding of a flat chip with a chip with etched grooves of nanometer depth. These nanochannels can be batch-fabricated and easily integrated with other components to make integrated nanofluidic devices. While other techniques may be available to make 2D nanochannels, we will only briefly introduce the two most common techniques, namely, those based on sacrificial lines and bonding because they can be readily made with easily accessible microfabrication facilities. 

FIGURE 2 Fabrication of heads for HDDs, (a) Thin film inductive and GMR heads are batch fabricated on ceramic wafers, (b) Wafers are sliced into rows. At the row level, the air bearing surface is first lapped to tight flatness specifications, and then lithographically patterned and etched to create air bearing features. Air bearing features are typically 0.1-2 om in height, (c) Finally, rows are parted into individual sliders 1 x 1.25 x 0.3 mm in size. SOURCE IBM. 

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