High Sensitivity Hard X-ray Detector for Characterization of Biological Systems

Advanced photon sources capable of providing intense X-ray beams over a wide energy range have proven to be outstanding resources for studying bio-energy processing-induced protein molecular structure changes in plant systems via static and time-resolved X-ray diffraction. The hard X-ray regime of the available flux also promises to significantly enhance the applicability of these sources to yield further advances in bio-energy sciences. Consequently, the past decade has seen significant improvements in the detector technology including the Mixed Mode Pixel Array Detector (MM-PAD), DECTRIS’s PILATUS, and TIMEPIX from MEDIPIX collaboration. All these detector platforms currently rely on the use of a Silicon, or a relatively thin CdTe semiconductor bump bonded to their respective readout platform. Although the use of CdTe extends the energy range of these detectors, further increase in energy performance is highly desirable. To address this issue, RMD proposes to develop an x-ray imaging platform based on TlBr semiconductor converter layer that can be directly deposited on a readout sensor using economical vapor deposition process. We plan to use the Timepix chip as the readout sensor for this purpose. With its extraordinarily high stopping power arising from its high effective atomic number (ZTl=81, ZBr = 35) and high density (7.6 gm/cm3), high resistivity, and excellent charge transport properties, particularly in thin layers, TlBr is extremely attractive for high resolution X-ray imaging even for energies well above 100 KeV. Low melting temperature of TlBr (480 °C) permits its thermal vapor deposition directly onto readout chips, thereby eliminating the need for bump bonding. Recently we have demonstrated efficacy of this approach which makes it worthy of pursuing from the technology development and commercialization perspective. The Phase I effort develops the design concept and the film deposition process and characterizes candidate TlBr films to demonstrate stability at operating bias with suitable electrode materials. The results of the Phase-I effort will be the design concept, the film deposition process as a flow chart, samples of films and the electrical and x-ray detector characterization of the films. The electrical characterization of the films includes measurements of the resistivity and the current voltage curves, and the radiological and stability characterization includes the measurement of x-rays in single pixels. TlBr films will be deposited on several Timepix chips and the resulting imaging x-ray detectors will be characterized. The Phase-II effort will further optimize the deposition process, deposit films on Timepix chips, characterize the imaging performance, and develop a readout platform suitable for structural biology applications at synchrotron facilities. Thus, the outcome of the proposed Phase I/Phase II program will be an advanced hard X-ray detector with high sensitivity for energies ranging from 8 keV to 100 keV and above that can operate at high global count rates with wide dynamic range, single photon sensitivity and high spatial and energy resolution. Commercial potential of such a detector is high and RMD will pursue that path. The proposed X-ray camera design will find use in virtually any situation where high-resolution X-ray imaging is desired or needed. A potential commercial application includes of dental radiography where high spatial resolution and contrast are required. An example is the nondestructive evaluation (NDE) of electronic circuitry, where feature sizes in integrated circuit interconnects (e.g., solder balls) can be on the order of only a few microns.