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Epitaxial GaN layers were implanted with radioactive 181 Hf ions in order to study the temperature dependence of the electric field gradient (EFG) at the site of the probes after rapid thermal annealing at 1273 K. Results are compared to recent measurements with the 111 In probe that showed a surprising reversible increase of the fraction of undisturbed substitutional probe atoms at measuring temperatures above room temperature (Lorenz et al., Appl Phys Lett 80:4531, 2002). After implantation and annealing the majority of 181 Hf atoms are incorporated into undisturbed substitutional lattice sites and experience an axial symmetric EFG with a quadrupole interaction frequency (QIF) of ∼336 MHz at RT and a low frequency distribution. At measuring temperatures between 20 and 1100 K the QIF increases linearly by ∼4% in good agreement with point charge model calculations taking into account the thermal lattice expansion. In contrast, measurements with the 111 In probe showed a strong increase by ∼50% of the QIF above RT. Additionally, unlike for 111 In, for measurements with 181 Hf the substitutional fraction stays unchanged for elevated measuring temperatures.

This paper presents the results of an advanced digital IRFPA-family developed by Fraunhofer IMS. The IRFPA-family compromises the two different optical resolutions VGA (640 x 480 pixel) and QVGA (320 x 240 pixel) by using a pincompatible detector board. The uncooled IRFPAs are designed for thermal imaging applications in the LWIR (8 .. 14µm) range with a full-frame frequency of 30 Hz and a high thermal sensitivity. The microbolometer with a pixel-pitch of 17µm consists of amorphous silicon as the sensing layer. By scaling and optimizing our previous microbolometer technology with a pixel-pitch of 25µm we enhance the thermal sensitivity of the microbolometer. The microbolometers are read out by a novel readout architecture which utilizes massively parallel on-chip Sigma-Delta-ADCs. This results in a direct digital conversion of the resistance change of the microbolometer induced by incident infrared radiation. To reduce production costs a chip-scale-package is used as vacuum package. This vacuum package consists of an IRtransparent window with an antireflection coating and a soldering frame which is fixed by a wafer-to-chip process directly on top of the CMOS-substrate. The chip-scale-package is placed onto a detector board by a chip-on-board technique. The IRFPAs are completely fabricated at Fraunhofer IMS on 8" CMOS wafers with an additional surface micromachining process. In this paper the architecture of the readout electronics, the packaging, and the electro-optical performance characterization are presented.

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In this paper a novel concept for the fabrication of highly sensitive uncooled microbolometers is presented. The approach is based on the realization of thermal isolation and simultaneous electrical contacting of the microbolometers by means of sufficiently long and thin coated nanotubes, which can be fabricated by post processing on top of CMOS wafers comprising the ROIC. Thus, the effective area of the absorption layer is maximized at a given pixel size, as lateral legs, which have been the main component of the thermal isolation commonly, are completely omitted. The resulting thermal conductance can be tuned independently from the pixel size by varying the geometry and structuring of the nanotubes. Based on test structures the nanotube microbolometers are characterized with respect to electro-optical and mechanical properties. The focus in this paper is on nanotube microbolometers with a pixel size of 12 μm