Active Pixel Sensors for direct detection of soft X-rays

The imaging of soft X-ray images is typically performed with charge coupled devices (CCDs). However, these can have limited readout speed, dynamic range and can also require significant cooling to obtain the required signal to noise ratio. Active pixel sensors (APS) are able to combine faster readout speeds and higher dynamic range with in-pixel intelligence to allow region of interest readout and adaptive gain. To obtain high detection efficiency and 100% pixel fill factor the sensor is back thinned and illuminated from the backside. We report on the characterization of a back-thinned APS (Vanilla); an array of 512 × 512 pixels of size 25 × 25 microns. The sensor has a 12-bit digital output for full frame mode, as well as being able to be readout in a fully programmable Region-Of-Interest (ROI) analogue mode. In full frame, the sensor can operate at a readout rate of more than 100 frames per second. Characterization of the detector was carried out through the analysis of photon transfer curves to yield measurements of the full well capacity, noise levels, gain constants and device linearity. Spectral response measurements were made to show the improvement in detection efficiency using a backthinned sensor. A typical synchrotron experiment was performed at the Diamond Light Source (DLS) using Soft X-rays ( ~ 700 eV) to produce a diffraction pattern from a permalloy sample. The pattern was imaged at a range of frame rates, up to 20Hz, and a range of temperatures for both a back-thinned Vanilla and a Princeton PIXIS-XO: 2048B CCD. The results of which are compared. The detection efficiency of the APS is shown to be comparable to the CCD for a given frame rate (0.1Hz), with similar noise levels. We suggest that the back-thinned APS are a viable technology choice for the direct detection of soft X-rays for synchrotron applications

Comparison of a CCD and an APS for soft X-ray diffraction

We compare a new CMOS Active Pixel Sensor (APS) to a Princeton Instruments PIXIS-XO: 2048B Charge Coupled Device (CCD) with soft X-rays tested in a synchrotron beam line at the Diamond Light Source (DLS). Despite CCDs being established in the field of scientific imaging, APS are an innovative technology that offers advantages over CCDs. These include faster readout, higher operational temperature, in-pixel electronics for advanced image processing and reduced manufacturing cost. The APS employed was the Vanilla sensor designed by the MI3 collaboration and funded by an RCUK Basic technology grant. This sensor has 520 x 520 square pixels, of size 25 μm on each side. The sensor can operate at a full frame readout of up to 20 Hz. The sensor had been back-thinned, to the epitaxial layer. This was the first time that a back-thinned APS had been demonstrated at a beam line at DLS. In the synchrotron experiment soft X-rays with an energy of approximately 708 eV were used to produce a diffraction pattern from a permalloy sample. The pattern was imaged at a range of integration times with both sensors. The CCD had to be operated at a temperature of -55°C whereas the Vanilla was operated over a temperature range from 20°C to -10°C. We show that the APS detector can operate with frame rates up to two hundred times faster than the CCD, without excessive degradation of image quality. The signal to noise of the APS is shown to be the same as that of the CCD at identical integration times and the response is shown to be linear, with no charge blooming effects. The experiment has allowed a direct comparison of back thinned APS and CCDs in a real soft x-ray synchrotron experiment

Technological inclusiveness: Northern versus Chinese induced technologies in the garment industry

The Northern economies have been the main sources of technologies for the global garment manufacturing industry. Over the past decade, China has become an important alternative source of these technologies offering a range of technological choices for small scale and dispersed production of cheap consumer goods, particularly in the developing world. Preceding a national foresight exercise aimed at enhancing the capabilities of small-scale garment producers in Uganda, we examine the potential ‘inclusiveness’ of garment sewing machines imported from the Northern economies and China, and their individual potential to enhance the capabilities of poor garment producers, particularly, women and rural dwellers. Data for our study included a survey and semi-structured interviews with 147 garment firms and other key informants. Compared to the Chinese sewing machines, we found that the Northern machines have high acquisition cost, relies on scale and advanced infrastructure, and tend to exclude poor rural producers (often women). The transfer of Chinese technologies to Uganda, we also found is much easier, have larger spread effects, leading to smaller gaps in technological know-how between China and Uganda because of the context in which Chinese technological innovations are induced. We conclude with some implication of our study to theory and policy