Chalcogenide Glass Radiation Sensor; Materials Development and Design and Device Testing Chalcogenide Glass Radiation Sensor; Materials Development and Design and Device Testing Whereas resistance changes are relatively simple to detect and measure, the device itself must be configured to take maximum advantage of the radiation effect. Hence, the first experimental task in this sub-program will be the design of device structures that will produce an appropriate degree of resistance change for a given dose. Two configurations will be examined in this respect: (1) Lateral devices consisting of coplanar electrodes on a layer of ChG, and (2) vertical devices in which a thin film of ChG is sandwiched between two electrodes. Examples of these two configurations are shown in Fig. 1. In the planar device of Fig. 1a, exposure causes lateral diffusion from the Ag electrode into the gap between the sensing electrodes which are made of a material, such as Ni, that will not react with the underlying glass during exposure. The initial resistance between these electrodes will be extremely high due to the low conductivity of the ChG but the higher the radiation dose, the greater the lateral diffusion of the Ag and this will result in a greater area of doped (high conductivity) ChG in the inter-electrode gap. In this manner, the device resistance will be progressively lowered during exposure. In the vertical device (Fig. 1b), the Ag diffuses into the undoped ChG from the top (Ag) electrode toward the bottom (Ni) electrode, thereby doping the glass and lowering the device resistance. This tructure may also be inverted so that the Ag electrode is on the bottom. Note that this device type should be the more sensitive of the two as the electrode spacing is determined by the thickness of the glass layer (which can be as thin as 10 nm) and hence even a small amount of Ag diffusion will cause a substantial change in resistance between the electrodes. On the downside, this device will have a smaller dynamic range, largely because of a lower initial resistance, and will also saturate more readily. However, since both sensors use the same materials, albeit in a different configuration, high and low dynamic range/sensitivity (lateral and vertical) devices may be fabricated on the same substrate to allow a larger range of doses to be measured accurately. The other aspect of device design lies with the choice of dimensions and the thicknesses of the ChG and Ag source/electrode layers in particular. Since little data exists on energy loss in such materials, a range of thicknesses of the various ChG and electrode layers will be employed in test devices to determine the effect of these parameters on sensitivity and other performance factors. Various device areas will also be investigated in both lateral and vertical devices. Both device types are reversible as far as the Ag dissolution effect is concerned, as negative bias on the Ag electrodes (with respect to the Ni electrodes) will cause the diffused material, which is in the form of Ag+ ions in the glass, to drift out of the material and redeposit at the Ag source. In the case of the lower resistance vertical device, it may also be possible to reverse some of the structural effects by applying a short current pulse after Ag removal to promote Joule heating in the glass, thereby annealing and returning it to its initial state. We intend to investigate both reversal mechanisms as part of the device characterization work.
|Effective start/end date||10/8/09 → 3/31/13|
- Battelle Energy Alliance: $480,000.00
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