Detector module for an X-ray detector system

Details Detector module for an X-ray detector system Detector module for an X-ray detector system

2002-04-08

2004-09-21

Hannaher, Constantine (Department: 2878)

Radiant energy

Invisible radiant energy responsive electric signalling

Semiconductor system

C250S366000

Reexamination Certificate

active

06794654

ABSTRACT:

The invention relates in general to a detector module for an X-ray detector system for use in X-ray holography and X-ray spectroscopy with atomic resolution as well as a modular X-ray detector system for the above applications in which such detector modules are used.
Since the invention of holography in 1948, work has been carried out on the application of the holography principle to the three-dimensional representation of atomic structures. A possible solution principle is based on the technique of X-ray holography.
In X-ray holography, atoms in a material sample to be examined are excited to fluorescence, and the fluorescence radiation from the material sample is recorded by a detector. The electric output signals of the detector, which reflect the interference field which builds up within the material sample, then give information about the three-dimensional structure of the examined sample material. For this purpose it is however necessary that the highest possible number of measurements be carried out on the material sample.
In the past few years, clear progress has been made in the development and production of X-ray detectors which are intended to record the fluorescence radiation of the material sample and separate this reliably from the varied background radiation. These detectors must on the one hand be energy-sensitive, in order to make possible a distinction of the incoming photons according to their energy or the wavelength of the radiation, but on the other hand, make it possible to operate up to such high counting rates that they record some hundreds of thousands of photons per second. For this purpose, in addition to silicon detectors, mostly germanium detectors were used in the past. The latter must however be cooled with liquid nitrogen, which is relatively costly, and are more suited to recording radiation from approximately 10 keV. A further disadvantage in the use of germanium detectors is that the electronics needed to amplify the measurement signals from the germanium detector can only be arranged at a position which is relatively remote from the germanium detector. To couple the germanium detector with the amplification electronics, long connection lines are thus required, which leads to strong interference and to a susceptibility to error. An integration of pre-amplifier stages in the vicinity of the germanium detector has to date not been successful, the costly cooling of the germanium detector representing a major obstacle. In addition, with an integration of the amplification electronics in the vicinity of the germanium detectors, a considerable number of signal lines must be routed away from the germanium detector or from the amplification electronics, which has proved to be an insurmountable obstacle even with smaller detector lines or detector arrays.
Very recently, progress has also been made in the development and production of location- and energy-resolving silicon X-ray detectors. Thus for example, the monolithic integration of highly sensitive drift detector cells with field effect transistors based on high-resistance silicon substrates was achieved. This detector type has already been used as a single-cell detector in the field of X-ray holography.
As mentioned above, it is necessary for X-ray holography that as large as possible a number of measurements of the material sample be carried out. In one of the possible concrete measurement processes (measurement process
1
), this means that a large number of measurements of the fluorescence radiation of the sample are carried out above the material sample over the solid angle region of a hemisphere above the material sample with an angular resolution in the degree range. With these measurements, it is necessary when using single-cell detectors to displace the detector, by means of a mechanically complex and costly displacement structure, stepwise along various tracks on the semi-spherical surface above the material sample. To be able to detect the characteristic lines within the spectrum with the required accuracy, approximately 2·10
6
entries per solid angle element are for example required. Up to an event rate of approximately 150 kHz, the lines can be determined without major adverse effect on their width. As, for example, 7200 recordings at different solid angles may be required for a complete hologram, a total measurement time of some 24 hours results.
In a second concrete measurement process (measurement process
2
) of X-ray holography, the required angular resolution is achieved through different arrival angles of monochromatic X-ray light. An angular resolution of the fluorescence radiation of the sample and thus a displacement of the detector is not required. Due to the abovementioned event-rate limitation of single-cell detectors, the same total measurement time results.
It is possible to shorten the long total measurement time by using multi-cell detectors instead of a single-cell detector. Through simultaneous measurement of different angle regions (measurement process
1
) or the event rate correspondingly multiplied in the case of multi-cell detectors, (measurement process
2
), the total measurement time is reduced by approximately the factor of the number of detector elements. Due to the limited number of cells or elements, all commercial multi-cell germanium detectors neither make costly displacement structures superfluous in measurement process
1
nor make possible a measurement time reduction to less than approximately one hour (both measurement processes). This reduction in measurement time is regarded as insufficient, as both (synchrotron) radiation sources and the detectors are subjected to fluctuations during long-time operation. The material sample itself can also change during this long measurement, for which reason real-time recordings are ideally desired.
In addition to the detailed example of X-ray holography presented here, detectors for X-ray radiation are used in many other measurement methods, for example in X-ray absorption spectroscopy, X-ray diffraction, X-ray fluorescence analysis and many more fields. For reasons comparable with those mentioned above, commercial silicon and germanium detectors limit the measurements in many applications (for example in synchrotron radiation sources) due to the maximum possible event rate of the detectors or the achievable angle or location resolution.
In U.S. Pat. No. 5,041,729, a multi-cell radiation detector is disclosed in which a number of detector elements is arranged in the form of a line. The radiation detector contains a scintillator on the rear side of which 12 lamellar photodiodes are arranged in the form of a line alongside each other. A holder is attached to the photodiodes by means of an isolating adhesive so that all 12 photodiodes are covered and an end section of each photodiode is exposed for wiring. The holder consists of a ceramic insulator and is equipped on its rear side with signal lines for each element. The bond-connection surface of each photodiode is connected by a wire bond to the signal lines. The disadvantage of this design is that only a detector line—but not a detector array—can be produced as the type of wiring allows exclusively a linear arrangement of the detector elements. When using a detector line however, a very long measurement time is required. In addition, the detector line must be displaced stepwise by means of a mechanically complex and costly displacement structure to carry out a complete recording.
It is therefore the object of the invention to provide a detector system with the help of which the above-mentioned disadvantages of the state of the art are overcome. It is in particular the object of the present invention to provide a detector module with a two-dimensional arrangement of detector elements forming a detector array including the corresponding wiring technique, the simultaneous recording of X-ray light being possible via a location or angular resolution, so that for example in X-ray holography, the otherwise customary displacement structure is superfluous. A further

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