Two-channel IR gas sensor with two detectors based on LiTaO3 single-crystal wafer

Keywords

• LiTaO₃ wafer;
• Gas cell structure;
• Gas sensor

An infrared (IR) single-element detector based on a lithium tantalate (LiTaO₃) single-crystal wafer has been successfully fabricated. The preparation and design of the device are discussed and analyzed in detail. The processing of a thin LiTaO₃ wafer, the characterization of an IR filter window, and the assembly of the wafer and filter are explained. A LiTaO3 sensor element, a CMOS amplifier, a narrow-band filter (which can be selected to operate within the appropriate spectral region), and the read-out circuits are set into a TO-18 vessel. Each TO-18-type detector offers a single channel (a single detection wavelength). Two TO-18 detectors with different filters, one acting as a detection channel and the other as a reference, a broadband light source, a circuit board and a flake of wire gauze are assembled and integrated into a gilded gas cell for the purpose of detecting ethene gas.


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Uniform growth and repeatable fabrication of inch-sized wafers of a single-crystal diamond

We conducted a repetitive process for tiling freestanding substrates made from one identical seed crystal. After the mechanical polishing of both sides of the tiled substrates over the inch-sized area, the boundaries between the constituent substrates were barely recognized. By repeating the tiling process, we succeeded in fabricating several freestanding wafers with a size of 1.5 in. (area of approximately 20 × 40 mm2). For this wafer size range, we found that non-uniformities in the morphology, as well as the growth rate, became remarkable. By qualitative comparison between the numerical predictions and the experimental observations, we discussed the dominant factors that control the non-uniformity.

Highlights:
► Inch size wafers of single-crystal diamond are fabricated.
► Such large size wafers are processed to enlarge the wafer size moreover.
► Finally, 1.5 inch size freestanding wafers are fabricated.
► Possible reasons of non-uniformity in impurity concentration are discussed.

Keywords:
Single-crystal diamond; Microwave plasma CVD; Lift-off processing; Mosaic wafers; Simulation

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