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This paper presents a microfabricated sensor that uses electrical microdischarges to sense the deflection of a diaphragm under applied pressure. The sensor responds by redistributing electron current of pulsed microdischarges between one cathode ( $K$ ), a reference anode (A1), and a deflecting anode (A2), all of which are located in a cavity under the diaphragm; the differential anode current indicates the applied pressure. In this paper, the sensor is monolithically fabricated from a single silicon wafer, using a combination of surface micromachining and through-wafer isolated bulk-silicon lead transfer (TWIST) technology. The TWIST technology provides lead transfer into the sealed cavity as well as backside contacts, allowing miniaturization of the device footprint and surface mount assembly within systems. The active footprint of the complete sensor measures 300\times 300 \,\,\mu \text {m}^{2} in size, making it the smallest sealed microdischarge-based pressure sensor reported to date. The normalized differential current from the anodes monotonically increases from −0.7 to 0.2 as the external pressure increases from 1 to 8 atm. [2017–0274] [ABSTRACT FROM PUBLISHER]

Microfabricated radiation detectors can be used to provide first alert information about presence of harmful radiation. This paper describes a micromachined gamma detector that operates in the Geiger–Muller (G–M) regime. Gamma rays eject photoelectrons from the cathode material through the photoelectric effect and/or Compton scattering, which in turn ionize the Ar fill-gas providing a current pulse. The detector utilizes cathode stacks that are micromachined from stainless steel #304 foil. Micromachined glass fingers with thin-film anode metal traces are positioned transversely through aligned perforations in the stacked cathodes. This orthogonal array of anodes and cathodes effectively distinguishes electron avalanche regions from drift regions despite the miniaturization, thereby reducing the likelihood of spurious discharges. Overall, the detector diameter and height are 9 and 2.5 mm, respectively. Detector performance is characterized using a 99- $\mu $ Ci 137Cs source placed at a distance of 3 cm from the detector. In an integration time of 10 min at an applied voltage of 630 V, a source:background ratio of 89:1 is achieved—a fivefold improvement over the previously reported micromachined devices operating in the G–M regime. This architecture also reduces the typical charge per discharge to 6.6 pC, allowing the estimated dead time between detection events to be $\sim 1 \mu $ s. [2014-0333] [ABSTRACT FROM PUBLISHER]

Microfabricated detectors can be used to provide first alert information about the presence of radiation sources. This paper describes a micromachined neutron detector that operates in the Geiger-Muller regime. It utilizes electrodes that are lithographically micromachined from 50- \mu \textm thick stainless steel #304 foil. The cathode is coated with a 2.9- \mu \textm thick layer of Gd on one side to convert thermal neutrons into fast electrons and gamma rays, which are then detected by ionization of the fill gas (Ar). Three electrodes are stacked in a cathode-anode-cathode arrangement, separated by 70- \mu \textm thick Kapton spacers, and assembled within a commercial TO-5 package. The detector diameter and height are 9 and 9.6 mm and it weighs 0.97 g. Detector performance is characterized using a 90 $\mu $ Ci 252Cf neutron source placed at a distance of 10 cm from the detector. Using Pb blocks between the source and detector to block gamma rays, the typical detector response at 285 V bias is \sim 8.7$ counts per minute (cpm), with background radiation count of 1.2 cpm. The typical dead time is 5.3 ms. Compared with commercial devices which operate at >900 V, have detector volumes of 2000–100000 mm ^{3} and can only detect a subset of radiation types (i.e., beta particles, gamma rays, and neutrons), this device offers lower operating voltages smaller volume and the ability to detect all three types of radiation. [ABSTRACT FROM PUBLISHER]

This paper investigates a miniaturized, chip-scale Penning cell array for sputter-ion pumping. In a 2.5 \cm^3 package, a 0.2 \cm^3 pump architecture with 1.5 mm diameter cells in a 4 \times 2 array reduces pressure from 1 Torr (133.3 Pa) to < 200 mTorr (26.6 Pa) in about 10 h, and from 115 mTorr (15.3 Pa) to < 10 mTorr (1.33 Pa) in 4 h. The rate of molecular removal in this range of pressures is 0.09 \times 10^13 to 1.17 \times 10^13 molecules/s. Experiments show that the architecture is capable of igniting and sustaining the plasma required for operating at a pressure at least as low as 1.5 \mu\Torr (200 nPa). The advantage of the Penning cell architecture reported here in comparison to other chip-scale ion pump architectures is the drastically reduced operating pressures that can be achieved and maintained. The microdischarge requires 450–600 V applied across the device and consumes 100–250 mW. The Penning cell array architecture shows significant promise for power efficient high-vacuum pumping in chip-scale and smaller systems.\hfill[2012-0133] [ABSTRACT FROM PUBLISHER]

This paper describes a microdischarge-based pressure sensor for harsh liquid environments that utilizes a ceramic package sealed with a deflecting diaphragm that also serves as a cathode. Located within the package is a reference cathode and an anode. The microdischarges are created between the two cathodes and the anode. The external pressure deflects the diaphragm, varying the interelectrode spacing and changing the differential current between the two competing cathodes. The electrodes are fabricated from a Ni foil and separated by dielectric spacers within a micromachined glass cavity. The structures are enclosed within a 1.6- \mm^3 ceramic surface mount package. Device sensitivity is approximately 4900 ppm/ \lbf/\in^2 (72 000 ppm/atm), and diaphragm displacement is approximately 0.15 \mu\m/atm. \hfill[2011-0308] [ABSTRACT FROM AUTHOR]

This paper reports deposition of silicon at elevated and room temperatures in spatially localized areas of a microchip by plasma-enhanced chemical vapor deposition using microplasmas. The microplasmas are generated by providing dc power to thin-film Ti electrodes patterned on the microchip. Electrode arrangements include configurations in which multiple cathode elements share a single anode. At the operating pressures used, the plasma glow is confined to the region directly over the energized cathodes only, and the deposition is localized to these regions. A silane ambient allows Si to be deposited at 6.7–15.9 nm/min using cathode power densities of 3.65–9.35 W/cm², with the substrate heated to 300 °C. At room temperature, deposition rates up to 4.2 nm/min are realized. Also described is a plasma-coupling technique that permits isolated metal pads to be powered by plasma spreading from a proximate cathode at certain levels of power and pressure. This permits controlled variations of silicon thickness in a subarray of unbiased electrodes, simplifying the powering scheme. [ABSTRACT FROM AUTHOR]