Microstrip Gas Counters

Microstrip Gas Counters

DOI: 10.4018/978-1-4666-6014-4.ch002
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In this chapter, the first micropattern gaseous detector, the microstrip gas counter, invented in 1988 by A. Oed, is presented. It consists of alternating anode and cathode strips with a pitch of less than 1 mm created on a glass surface. It can be considered a two-dimensional version of a multiwire proportional chamber. This was the first time microelectronic technology was applied to manufacturing of gaseous detectors. This pioneering work offers new possibilities for large area planar detectors with small gaps between the anode and the cathode electrodes (less than 0.1 mm). Initially, this detector suffered from several serious problems, such as charging up of the substrate, discharges which destroyed the thin anode strips, etc. However, by efforts of the international RD28 collaboration hosted by CERN, most of them were solved. Although nowadays this detector has very limited applications, its importance was that it triggered a chain of similar developments made by various groups, and these collective efforts finally led to the creation of a new generation of gaseous detectors-micropattern detectors.
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2. Microstrip Gas Counters Manufacturing

Microstrip gas counters (MSGC) are manufactured using standard microelectronic technology. First a photo mask of the desired electrode structure is developed. This mask is placed on a metallized substrate. Two main methods were used for forming the conducting patterns: etching and so called lift-off technique.

With the etching method, a metal coated substrate (usually glass) is covered with a thin layer of photosensitive resin. It is exposure to ultraviolet (UV) light through the mask. The UV affected area is then chemically removed. Then the substrate is etched to eliminate the metal from the uncoated areas. Alternatively the same can be achieved by plasma etching. Then the residual resin is removed and the detector surface was carefully cleaned from residuals (Figure 1).

Figure 1.

Schematic presentation of two methods used for manufacturing of MSGCs: a) etching, b) lift –of method (Sauli, 1999).

With the lift-off method, a metallized substrate is illuminated by UV light through a negative photo mask (the mask in which previously opaque regions were made transparent and the transparent regions opaque). Then the photoresist from the exposed area is removed and the surface is coated with a metal film. After that the detector is etched to remove the remaining photoresist and the metal layers above it peels off. Finally, another etching removes the adhesion metal layer in the open regions. As a result, on the dielectric surface a metallic pattern is manufactured as exemplified in Figure 2.

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