Fully Depleted, Monolithic Pinned Photodiode CMOS Image Sensor Using Reverse Substrate Bias

A new pixel design using pinned photodiode (PPD) in a 180 nm CMOS image sensor (CIS) process has been developed as a proof of principle. The sensor can be fully depleted by means of reverse bias applied to the substrate, and the principle of operation is applicable to very thick sensitive volumes. Additional n-type implants under the in-pixel p-wells have been added to the manufacturing process in order to eliminate the large parasitic substrate current that would otherwise be present in a normal device. The new design exhibits nearly identical electro-optical performance under reverse bias as the reference PPD pixel it is based on, and the leakage current is effectively suppressed. The characterisation results from both front- and back-side illuminated sensor variants show that the epitaxial layer is fully depleted

Modelling electron distributions within ESA's Gaia satellite CCD pixels to mitigate radiation damage

The Gaia satellite is a high-precision astrometry, photometry and spectroscopic ESA cornerstone mission, currently scheduled for launch in 2012. Its primary science drivers are the composition, formation and evolution of the Galaxy. Gaia will achieve its unprecedented positional accuracy requirements with detailed calibration and correction for radiation damage. At L2, protons cause displacement damage in the silicon of CCDs. The resulting traps capture and emit electrons from passing charge packets in the CCD pixel, distorting the image PSF and biasing its centroid. Microscopic models of Gaia's CCDs are being developed to simulate this effect. The key to calculating the probability of an electron being captured by a trap is the 3D electron density within each CCD pixel. However, this has not been physically modelled for the Gaia CCD pixels. In Seabroke, Holland & Cropper (2008), the first paper of this series, we motivated the need for such specialised 3D device modelling and outlined how its future results will fit into Gaia's overall radiation calibration strategy. In this paper, the second of the series, we present our first results using Silvaco's physics-based, engineering software: the ATLAS device simulation framework. Inputting a doping profile, pixel geometry and materials into ATLAS and comparing the results to other simulations reveals that ATLAS has a free parameter, fixed oxide charge, that needs to be calibrated. ATLAS is successfully benchmarked against other simulations and measurements of a test device, identifying how to use it to model Gaia pixels and highlighting the effect of different doping approximations.Comment: 12 pages, 6 figures, appearing in Proc. of SPIE Optics and Photonics Conference (Focal Plane Arrays for Space telescopes IV), 2-6 August 2009, San Diego, US

Evaluation of valued youth: a national peer-tutoring programme to increase self confidence and motivation

Established first in the USA, Valued Youth has operated in the UK since 1996, and is currently implemented in about 50 schools in 8 regions. The programme is intended to help secondary school students who are at risk of disengaging with school or underperforming for a variety of reasons. These students are selected as tutors, given training on how to work with younger children and placed in a local primary school where they support pupils' learning. Valued Youth can be seen as one of many initiatives in secondary schools on re-engagement in learning and contributes to the UK government strategy of extending opportunities and providing flexible learning experiences to meet individual learners' needs and aptitudes. Evidence from the USA has shown the value of the programme in reducing drop-out, strengthening youngsters' perceptions of self and school, and reducing disciplinary referrals and absenteeism. The evaluation discussed in this paper considers the effect of the programme in a UK context, not only in terms of young people's attendance, attainment and confidence, but also in terms of what sort of youngsters seem to benefit and the effects of financial rewards, if any, on the outcomes. The paper reports on the first year of a two-year evaluation. Data were obtained from a pre- and post-questionnaire survey among tutors, a workshop with coordinators and visits to selected case study schools in several regions. Almost all tutors enjoyed the programme and would recommend the experience to others. There was a relatively low dropout and the programme was warmly appreciated by participating primary schools. We have evidence that Valued Youth markedly raises confidence, improves communication skills and keeps some at risk youngsters on track in school. Many types of youngsters benefit from the experience; those who lack confidence and have poor communication skills seem to make the most progress. Successful tutors tend to be those who are committed to the programme, willing to learn, are flexible and cooperative, and have some ability to interact with others, particularly children and primary teachers.</p

Evaluating teachers' and trainers' development in a large scale curriculum development project in South Yorkshire

The evaluative research upon which the paper is based focuses on the first three years of a six-year project “Pathways to Success” (PW) currently taking place in South Yorkshire and funded by the European Social Fund (ESF) as part of the Objective 1 programme from 2001-2007. Matched funding has been provided by schools, colleges and LEAs. The PW project is concerned with developing innovative curricula to raise achievement and improve youngsters' employability skills. The project is set in the context of regional regeneration in an area where unemployment is higher than the European (and national) average, due to the decline of traditional steel and coal industries and where the gross domestic product is less than 75% of the European average. South Yorkshire is also an area where overall achievement in schools at all stages is lower than the national average and participation in post-16 education and higher education is persistently below national figures. Although employment is slowly rising due to reorientation from manufacturing towards a service and knowledge-based economy, pockets of severe unemployment and deprivation remain and are among the ten worst in the country.</p

New Pathways: evaluating the implementation of a major work- related programme in Northern England

The evaluative research upon which this paper is based is focussed on the implementation of a three-year programme “Pathways to Success” (usually shortened to “Pathways”) in South Yorkshire, England. It is part of a much larger regional regeneration project funded by the European Social Fund (ESF) from 2001-2004. The Pathways programme is concerned with developing innovative curricula for the 14-19 age range in four Local Education Authorities (LEAs)1 and is taking place in 76 secondary (high) schools. A team from Sheffield Hallam University was responsible for evaluating the success of the Pathways programme and our findings reported here refer to the first year of implementation.</p

Genetic algorithms: a pragmatic, non-parametric approach to exploratory analysis of questionnaires in educational research

Data from a survey to determine student attitudes to their courses are used as an example to show how genetic algorithms can be used in the analysis of questionnaire data. Genetic algorithms provide a means of generating logical rules which predict one variable in a data set by relating it to others. This paper explains the principle underlying genetic algorithms and gives a non-mathematical description of the means by which rules are generated. A commercially available computer program is used to apply genetic algorithms to the survey data. The results are discussed

Quantum phase transitions in the Fermi-Bose Hubbard model

We propose a multi-band Fermi-Bose Hubbard model with on-site fermion-boson conversion and general filling factor in three dimensions. Such a Hamiltonian models an atomic Fermi gas trapped in a lattice potential and subject to a Feshbach resonance. We solve this model in the two state approximation for paired fermions at zero temperature. The problem then maps onto a coupled Heisenberg spin model. In the limit of large positive and negative detuning, the quantum phase transitions in the Bose Hubbard and Paired-Fermi Hubbard models are correctly reproduced. Near resonance, the Mott states are given by a superposition of the paired-fermion and boson fields and the Mott-superfluid borders go through an avoided crossing in the phase diagram.Comment: 4 pages, 3 figure