The demand for higher resolution x-ray optics (a few arcseconds or better) in the areas of astrophysics and solar science has, in turn, driven the development of complementary detectors. These detectors should have fine pixels, necessary to appropriately oversample the optics at a given focal length, and an energy response also matched to that of the optics. Rutherford Appleton Laboratory have developed a 3-side buttable, 20 mm x 20 mm CdTe-based detector with 250 μm square pixels (80x80 pixels) which achieves 1 keV FWHM @ 60 keV and gives full spectroscopy between 5 keV and 200 keV. An added advantage of these detectors is that they have a full-frame readout rate of 10 kHz. Working with NASA Goddard Space Flight Center and Marshall Space Flight Center, 4 of these 1mm-thick CdTe detectors are tiled into a 2x2 array for use at the focal plane of a balloon-borne hard-x-ray telescope, and a similar configuration could be suitable for astrophysics and solar space-based missions. This effort encompasses the fabrication and testing of flightsuitable front-end electronics and calibration of the assembled detector arrays. We explain the operation of the pixelated ASIC readout and measurements, front-end electronics development, preliminary X-ray imaging and spectral performance, and plans for full calibration of the detector assemblies. Work done in conjunction with the NASA Centers is funded through the NASA Science Mission Directorate Astrophysics Research and Analysis Program.
HAPEX is an artificial bone analogue composite based on hydroxyapatite and polyethylene, which can be applied for growth of bone cells. Due to its biocompatibility and favourable mechanical properties, HAPEX is used for orthopaedic implants like tympanic (middle ear) bones.
The morphology of HAPEX surfaces is of high interest and it is believed that surface structuring on a micron scale might improve the growth conditions for bone cells. A new and simple approach for the microstructuring of HAPEX surfaces has been investigated using LIGA technique.
LIGA is a combination of several processes, in particular lithography, electroplating and forming/moulding. For HAPEX surface structuring, arrays of dots, grids and lines with typical lateral dimension ranging from 5 μm to 50 μm were created on a chromium photomask and the patterns were transferred into thick SU-8 photoresist (structure height > 10 μm) by UV lithography. Subsequently, the SU-8 structures served as moulds for electroplating nickel on Si wafers and nickel substrates. The final nickel microstructures were used as embossing master for the HAPEX material. Embossing was carried out using a conventional press (> 500 hPa) with the facility to heat the master and the HAPEX. The temperature ranged from ambient to a few degrees above glass transition temperature (Tg) of HAPEX. The paper will include details of the fabrication process and process tolerances in lateral and vertical directions. Data obtained are correlated to the temperature used during embossing.
Some of the most important steps in manufacturing microelectromechnical systems (MEMS) are their assembly and handling. With handling we mean the way we can safely, without damages, pick microparts of any shape or any kind of material, rotate them to the desired orientation and finally position them precisely on or connect them with other microparts. For these purposes, specially designed tools – microgrippers – are required. This paper presents the design, development, fabrication method using the SU8 technology and post-fabrication processes with the goal to obtain a new type of micro-gripper. This micro-gripper was produced for a handling and assembly station developed at the IMFT (TU Wien). To investigate the obtained structures we performed a "quality inspection" and a calibration of the gripper parameters. These investigations gave an important insight on such parameters as technology accuracy, parameter settings for the SU8 technology, the obtained properties of the structure and the functional features (elasticity and applied force). Based on this, possibilities for further quality improvements have been considered.
LIGA is a technology that offers significant advantages where high accuracy, high aspect ratio microstructures are required. The application of LIGA to the manufacture of real products has been delayed by technical problems that exist with the individual process steps and the limited availability of integrated facilities, enabling users to subcontract the complete manufacturing process. These problems have been dominated by the limited availability of high quality masks, long and expensive exposure at synchrotron radiation sources and the electrodeposition of thick stress-free layers. This paper describes the practical solutions developed at the Central Microstructure Facility, RAL, for the key process steps of manufacturing high precision gold-on- beryllium masks, exposure of SU-8 resist using a 2 GeV synchrotron, electrodeposition of deep ($GTR 500 mm), stress-free metal layers and resist stripping procedures fro 3 micrometers minimum features up to 500 mm deep on 4-6 inch wafers. A cost model shows that the reduction in the exposure time using SU-8 instead of PMMA resist may enable x-ray LIGA to be cost competitive with other techniques such as uv LIGA, DRIE or direct laser ablation.
Although the process of deep x-ray lithography with PMMA achieves good resolution, it requires significant exposure times because of the low sensitivity of PMMA to x-rays. Therefore resist materials, which can achieve high resolution, but which are inherently more sensitive than PMMA, are desirable. Here it is shown, that x-ray exposures of the SU-8 resist can achieve high resolution with substantially reduced exposure times. Irradiation at the synchrotron source of DCI at Lure (Paris) and MAXLAB (Lund, Sweden) demonstrated a reduced exposure time for a 600 micrometers thick SU-8 relative to PMMA. The does needed to obtain standing structures was 30 J/Cm3 for DCI and 52 J/CM3 for MAXLAB. A 600 micrometers thick PMMA resist requires a typical bottom does of 4 kJ/cm3, so Su-8 is considerably more sensitive to x-rays than PMMA. Preliminary critical dimension measurements (CD) of the 600 micrometers SU-8 resist structures have been obtained for the entire height of the structure, which was exposed at DCI. The CD measurements were made in a Scanning Electron Microscope (SEM) using 10 micrometers wide structures, which have a 20micrometers pitch, this being used to calibrate the measurements. These measurements show that the gain in the critical dimension per structure edge is dependent on the bottom dose. Doses of 30 J/cm3 achieved a CD gain per edge of +0.5 micrometers , while doses of 40 J/cm3 Yielded a CD gain per edge of 0.9 micrometers . However, the gain in the CD per edge is critically dependent on the solvent content in the resist. Doses of 40 J/cm3 into a resist with a 2% residual solvent content yielded CD gains per edge of 0.3micrometers . In addition, the dose profile in the resist does not change the CD values significantly. It has been shown that the resolution of the x-ray exposed SU-8 structures compare quite favorable with PMMA, but the exposure time for SU-8 is approximately 100 times less than that for PMMA. This significantly improves throughput for deep x-ray lithography processes.
Patterning of thick layer SU-8 photoresist has been investigated with different radiation sources, including electron beam, X-ray, i-line stepper, UV mercury lamp with collimator, as well as two different types of UV contact maskaligner. Feature profiles with thickness up to 1 mm have been compared. Among all the radiation sources, x-ray exposure from a synchrotron radiation source is found to produce the best feature dimension control and has the highest feature aspect ratio. I-line stepper can also produce features with steep side wall but is limited to less than 200 micrometers resist thickness. The illumination parallelism is the key to control the resist profile, no matter what radiation sources are used. Other issues such as process condition become important when resist layer thickness is over 500 micrometers . Conditions for better profile control with thicker layer SU-8 photoresist are suggested.