SCUBA-2 is a revolutionary 10,000 pixel wide-field submillimetre camera, recently commissioned and now operational
at the James Clerk Maxwell Telescope (JCMT). Twin focal planes each consist of four 32 by 40 sub-arrays of
superconducting Transition Edge Sensor (TES) bolometers, the largest combined low temperature bolometer arrays in
operation, to provide simultaneous imaging at wavelengths of 450 and 850 microns. SCUBA-2 was designed to map
large areas of sky more than 100 times faster than the original ground breaking SCUBA instrument and has achieved this
goal. In this paper we describe the performance of the instrument and present results of characterising the eight science
grade TES bolometer arrays. We discuss the steps taken to optimise the setup of the TES arrays to maximise mapping
speed and show how critical changes to the sub-array module thermal design, the introduction of independent focal plane
and 1K temperature control and enhancements to the cryogenics have combined to significantly improve the overall
performance of the instrument.
The Smart X-Ray Optics (SXO) project comprises a UK-based consortium developing active/adaptive micro-structured
optical arrays (MOAs). MOA devices are designed to focus X-rays using grazing incidence reflection through
consecutive aligned arrays of microscopic channels. Adaptability is achieved using a combination of piezoelectric
actuators, which bend the edges of the silicon chip, and a spider structure, which forms a series of levers connecting the
edges of the chip with the active area at the centre, effectively amplifying the bend radius.
The spider actuation concept, in combination with deep silicon etching stopped close to the surface, can also be used to
create deformable mirrors where the curvature and tip/tilt angles of the mirror can be controlled. Finite Element Analysis
(FEA) modelling, carried out for the optimization of the spider MOA device, indicates that deformable mirrors with
curvature varying from flat to 5cm ROC and control over the tip/tilt angles of the mirror of +/-3mrad could be achieved.
Test spider structures, manufactured using a Viscous Plastic Processing Process for the PZT piezoelectric actuators and a
single wet etch step using <111> planes in a (110) silicon wafer for both the silicon channels and the spider structure,
have been bent to a radius of curvature smaller than 5 cm.
This paper evaluates the spider MOA's concept as a means to achieve deformable mirrors with controllable ROC and
control over the tip/tilt angles. FEA modelling results are compared with obtained characterization data of prototype
structures. Finally, manufacturing and integration methods and design characteristics of the device, such its scalability,
are also discussed.
The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing active/adaptive micro-structured
optical arrays (MOAs). These devices are designed to focus X-rays using grazing incidence reflection through
consecutive aligned arrays of microscopic channels etched in silicon. Adaptability is achieved using a combination of
piezoelectric actuators, which bend the edges of the silicon chip, and a spider structure, which forms a series of levers
connecting the edges of the chip with the active area at the centre, effectively amplifying the bend radius. Test spider
structures, have been bent to a radius of curvature smaller than 5 cm, indicating that in complete devices a suitable focal
length using a tandem pair configuration could be achieved.
Finite Element Analysis (FEA) modelling has been carried out for the optimization of the spider MOA device design.
Prototype devices have been manufactured using a Viscous Plastic Processing technique for the PZT piezoelectric
actuators, and a single wet etch step using {111} planes in a (110) silicon wafer for both the silicon channels and the
spider structure. A surface roughness of 1.2 nm was achieved on the silicon channel walls.
Characterisation techniques have been developed in order to evaluate the device performance in terms of the bending of
the MOA channels produced by the actuators. This paper evaluates the progress to date on the development of spider
MOA's comparing FEA modelling with the results obtained for prototype structures.
SCUBA-2 is a state of the art 10,000 pixel submillimeter camera installed and being commissioned at the James Clerk
Maxwell Telescope (JCMT) providing wide-field simultaneous imaging at wavelengths of 450 and 850 microns. At each
wavelength there are four 32 by 40 sub-arrays of superconducting Transition Edge Sensor (TES) bolometers, each
packaged with inline SQUID multiplexed readout and amplifier. In this paper we present the results of characterising
individual 1280 bolometer science grade sub-arrays, both in a dedicated 50mk dilution refrigerator test facility and in the
instrument installed at the JCMT.
The Smart X-Ray Optics (SXO) project comprises a U.K.-based consortium developing active/adaptive micro-structured
optical arrays (MOAs). These devices are designed to focus X-rays using grazing incidence reflection through
consecutive aligned arrays of microscopic channels etched in silicon. The silicon channels have been produced both by
dry and wet etching, the latter providing smoother channel walls. Adaptability is achieved using piezoelectric actuators,
which bend the device and therefore change its focal distance. We aim to achieve a 5 cm radius of curvature which can
provide a suitable focal length using a tandem pair MOA configuration.
Finite Element Analysis (FEA) modelling has been carried out for the optimization of the MOA device design, consider
different types of actuators (unimorph, bimorph and active fibre composites), and different Si/piezoelectric absolute and
relative thicknesses. Prototype devices have been manufactured using a Viscous Plastic Processing Process for the
piezoelectric actuators and dry etched silicon channels, bonded together using a low shrinkage adhesive. Characterisation
techniques have been developed in order to evaluate the device performance in terms of the bending of the MOA
channels produced by the actuators. This paper evaluates the progress to date on the actuation of the MOAs, comparing
FEA modelling with the results obtained for different prototype structures.
Piezoelectric actuators are widely employed in adaptive optics to enable an actively controlled mirror surface and
improve the optical resolution and sensitivity. Currently two new prototype adaptive X-ray optical systems are under
development through the Smart X-ray Optics project in a UK based consortium. One proposed technology is micro-structured
optical arrays (MOAs) which uses aligned micro-channels structures obtained by deep silicon etching using
both dry and wet techniques and bonded piezoelectric actuators to produce a micro-focused X-ray source for biological
applications. The other technology is large scale optics which uses a thin shell mirror segment with 20-40 bonded piezo-actuators
for the next generation of X-ray telescopes with an aim to achieve a resolution greater than that currently
available by Chandra (0.5").
The Functional Materials Group of Birmingham University has the capability of fabricating a wide range of piezo-actuators
including, for example, unimorph, bimorph and active fibre composites (AFC) by using a viscous plastic
processing technique. This offers flexibility in customising the shapes (from planar to 3-D helix) and feature sizes (>20
μm) of the actuators, as well as achieving good piezoelectric properties. PZT unimorph actuators are being developed in
this programme according to the design and implementation of the proposed mirror and array structures. Precise
controls on the dimension, thickness, surface finishing and the curvature have been achieved for delivering satisfactory
actuators. Results are presented regarding the fabrication and characterisation of such piezo-actuators, as well as the
progress on the large optic and MOAs prototypes employing the piezo-actuators.
The UK Smart X-Ray Optics consortium is developing novel reflective adaptive/active x-ray optics for small-scale laboratory applications, including studies of radiation-induced damage to biological material. The optics work on the same principle as polycapillaries, using configured arrays of channels etched into thin silicon, such that each x-ray photon reflects at most once off a channel wall. Using two arrays in succession provides two reflections and thus the Abbe sine condition can be approximately satisfied, reducing aberrations. Adaptivity is achieved by flexing one or both arrays using piezo actuation, which can provide further reduction of aberrations as well as controllable focal lengths. Modelling of such arrays for used on an x-ray microprobe, based on a microfocus source with an emitting region approximately 1μm in diameter, shows that a focused flux approximately two orders of magnitude greater than possible with a zone plate of comparable focal length is possible, assuming that the channel wall roughness is less than about 2nm.
The Smart X-ray Optics (SXO) programme is developing advanced active-adaptive optics for X-rays. There are two
main themes: large optics for applications in astronomy and small scale optics for micro-probing of biological cells and
tissue samples using Ti or Cr Kα radiation (4.5keV and 5.4keV, respectively) in studies related to radiation induced
cancers. For the latter objective, microstructured optical arrays (MOAs) have been proposed. These consist of an array of
channels deep etched in silicon. They use grazing incidence reflection to focus the X-rays through consecutive aligned
arrays of channels, ideally reflecting once off a channel wall in each array. Bending the arrays allows variable focal
length. The adaptivity is achieved by flexing the arrays using PZT (Lead Zirconate Titanate)-based piezo actuators.
The array bending has been modelled using finite element analysis (FEA) and the results showed that for reasonable
efficiency, the wall roughness of the channels should not exceed 2nm.
This paper describes two techniques of fabrication the MOAs: dry etching and wet etching. The first method requires a
special equipment called "inductively coupled plasma" (ICP) using Bosch processes that are designed to produce
features with a high aspect ratio with vertical walls. The second method involves using an alkaline solution for etching
<110> silicon wafers. This type of wafer was selected because of the large wet etch ratio between the (111) and (100)
planes that leads to smooth vertical walls. For our application tetra-methyl-ammonium hydroxide (TMAH) was used as it
is fully compatible with CMOS integrated circuit processes.
The UK Smart X-Ray Optics programme is developing the techniques required to both enhance the performance of
existing X-ray systems, such as X-ray telescopes, while also extending the utility of X-ray optics to a broader class of
scientific investigation. The approach requires the control of the inherent aberrations of X-ray systems using an
active/adaptive method. One of the technologies proposed to achieve this is micro-structured optical arrays, which use
grazing incidence reflection through consecutive aligned arrays of channels. Although such arrays are similar in concept
to polycapillary and microchannel plate optics, they are more flexible. Bending the arrays allows variable focal length,
while flexing parts of them provides adaptive or active systems. Custom configurations can be designed, using ray
tracing and finite element analysis, for applications from sub-keV to several-keV X-rays. The channels may be made
using deep silicon etching, which can provide appropriate aspect ratios, and flexed using piezo actuators. An exemplar
application will be in the micro-probing of biological cells and tissue samples using Ti Kα radiation (4.5 keV) in studies
related to radiation induced cancers.
SCUBA-2 is an innovative 10,000 pixel submillimeter camera due to be delivered to the James Clerk Maxwell Telescope in late 2006. The camera is expected to revolutionize submillimeter astronomy in terms of the ability to carry out wide-field surveys to unprecedented depths addressing key questions relating to the origins of galaxies, stars and planets. This paper presents an update on the project with particular emphasis on the laboratory commissioning of the instrument. The assembly and integration will be described as well as the measured thermal performance of the instrument. A summary of the performance results will be presented from the TES bolometer arrays, which come complete with in-focal plane SQUID amplifiers and multiplexed readouts, and are cooled to 100mK by a liquid cryogen-free dilution refrigerator. Considerable emphasis has also been placed on the operating modes of the instrument and the "common-user" aspect of the user interface and data reduction pipeline. These areas will also be described in the paper.
We present the results of characterization measurements on a 1280 pixel superconducting bolometer array designed for operation at wavelengths around 450 μm. The array is a prototype for the sub-arrays which will form the focal plane for the SCUBA-2 sub-mm camera, being built for the James Clerk Maxwell Telescope (JCMT) in Hawaii. With over 10 000 pixels in total, it will provide a huge improvement in both sensitivity and mapping speed over existing instruments. The array consists of molybdenum-copper bi-layer TES (transition edge sensor) pixels, bonded to a multiplexer. The detectors operate at a
temperature of approximately 175 mK, and require a heat sink at a temperature of approximately 60 mK. In contrast to previous TES arrays, the multiplexing elements are located beneath each pixel (an "in-focal plane" configuration). We present the results of electrical and optical measurements, and show that the optical NEP (noise equivalent power) is less than 1.4 × 10-16 W Hz-0.5 and thus within the goal of 1.5 × 10-16 W Hz-0.5.
SCUBA-2 is the next-generation replacement for SCUBA (Sub-millimetre
Common User Bolometer Array) on the James Clerk Maxwell Telescope. Operating at 450 and 850 microns, SCUBA-2 fills the focal plane of the telescope with fully-sampled, monolithic bolometer arrays. Each SCUBA-2 pixel uses a quarter-wave slab of silicon with an implanted resistive layer and backshort as an absorber and a superconducting transition edge sensor as a thermometer. In order to verify and optimize the pixel design, we have investigated the electromagnetic behaviour of the detectors, using both a simple transmission-line model and Ansoft HFSS, a finite-element electromagnetic simulator. We used the transmission line model to fit transmission measurements of doped wafers and determined the correct implant dose for the absorbing layer. The more detailed HFSS modelling yielded some unexpected results which led us to modify the pixel design. We also verified that the detectors suffered little loss of sensitivity for off-axis angles up to about 30 degrees.
SCUBA-2, which replaces SCUBA (the Submillimeter Common User Bolometer
Array) on the James Clerk Maxwell Telescope (JCMT) in 2006, is a
large-format bolometer array for submillimeter astronomy. Unlike previous detectors which have used discrete bolometers, SCUBA-2 has two dc-coupled, monolithic, filled arrays with a total of ~10,000 bolometers. It will offer simultaneous imaging of a 50 sq-arcmin field of view at wavelengths of 850 and 450 microns. SCUBA-2 is expected to have a huge impact on the study of galaxy formation and evolution in the early Universe as well as star and planet formation in our own Galaxy. Mapping the sky to the same S/N up to 1000 times faster than SCUBA, it will also act as a pathfinder for the new submillimeter interferometers such as ALMA. SCUBA-2's absorber-coupled pixels use superconducting transition edge sensors operating at 120 mK for performance limited by the sky background photon noise. The monolithic silicon detector arrays are deep-etched by the Bosch process to isolate the pixels on silicon nitride membranes. Electrical
connections are made through indium bump bonds to a SQUID time-domain multiplexer (MUX). We give an overview of the SCUBA-2 system and an update on its status, and describe some of the technological innovations that make this unique instrument possible.
The realization of a large (40x32) pixel sub-array on a 3-inch silicon wafer brings unique challenges involving the integration of a variety of microfabrication techniques. Design, development and fabrication procedures are described, with conventional MEMS
techniques in silicon being used where possible. High resolution imaging in the sub-millimetre range requires a pixel size of the order of one millimetre with a high signal/noise ratio detector,
which must be addressed at cryogenic temperatures via a very low noise amplifying system. This has been realized using a combination of Transition Edge Sensors (TES) with amplification and multiplexing (MUX) by Superconducting Quantum Interference Devices (SQUID), which imposes particular requirements in the method of construction. This paper describes the details of the technologies used to overcome the conflicting demands of the different elements. The need to operate
at millikelvin temperatures limits the materials that can be selected. Particular attention has been paid to the stresses induced in the structure by overlying films, bump bonding and any thermal processing.
SCUBA-2 is a second generation, wide-field submillimeter camera under development for the James Clerk Maxwell Telescope. With over 12,000 pixels, in two arrays, SCUBA-2 will map the submillimeter sky ~1000 times faster than the current SCUBA instrument to the same signal-to-noise. Many areas of astronomy will benefit from such a highly sensitive survey instrument: from studies of galaxy formation and evolution in the early Universe to understanding star and planet formation in our own Galaxy. Due to be operational in 2006, SCUBA-2 will also act as a "pathfinder" for the new generation of submillimeter interferometers (such as ALMA) by performing large-area surveys to an unprecedented depth. The challenge of developing the detectors and multiplexer is discussed in this paper.
Tristate antiferroelectric and v-shaped liquid crystal materials have recently offered the promise of both the fast switching of ferroelectric materials and the analogue switching of nematic materials at drive voltages compatible with those available from standard CMOS technology thereby making them, at least in principle, suitable for consideration in microdisplay and other photonic applications. AFLC development is in its early stages and the materials are not yet mature enough for widespread commercial use. The object of the ESPRIT funded MINDIS project has been to evaluate AF-LCoS technology. The electro-optical characteristics of a number of experimental materials have been experimentally measured in test cells that emulate the situation of a silicon backplane (e.g., aluminum reflective back electrode etc). Some candidate materials been shown to exhibit high contrast, uniformity and repeatability. A CMOS active matrix backplane with 1000 line resolution has been designed and fabricated. The backplane is capable of operating in digital or analogue modes for FLC and AFLC respectively. Planarization techniques have been applied to the CMOS wafers but planarization has been shown to be more problematic than with previous backplanes. The reasons for this are discussed. The technology has been theoretically evaluated for use in microdisplays for both projection and near-to-eye applications.
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