Design and Evaluation of a 2D Array PIN Photodiode Bump Bonded to Readout IC for the Low Energy X-ray Detector

A 2D array radiation sensor, consisting of an array of PIN Photodiodes bump bonded to readout integrated circuit (IC), has been developed for operation with low energy X-rays. The PIN photodiode array and readout IC for this system have been fabricated. The main performance measurements are the following: a few pA-scale leakage current, 350pF junction capacitance, 30�√ -depth depletion layer and a 250�√ intrinsic layer at zero bias. This PIN photodiode array and readout IC were fabricated using a PIN photodiode process and standard 0.35�√ CMOS technology, respectively. The readout circuit is operated from a 3.3V single power supply. Finally, a 2D array radiation sensor has been developed using bump bonding between the PIN photodiode and the readout electronics. HIS paper reports on a study of digital X-ray imaging for general radiography. The study is based on an X-ray imager that uses a 2D array PIN photodiode with bump bonding to a CSA (Charge Sensitive Amplifier) with an ASIC (Application Specific Integrated Circuit) for low energy detection. 2-D digital radiation sensors such as the CZT, CdTe and a-Se have disadvantages that include difficulty of viewing a large field, high cost, and the requirement for high voltage as compared to indirect radiation type sensors. These disadvantages are in spite of a direct type detector and 100% fill factor. Additional problems are the sensor's sensitivity to temperature and flat panel distortion. The CCD is difficult to view in a large field and has high cost. Moreover, for the CCD system, front-end electronics are needed for the design of each individual system. The CMOS sensor is a low cost and monolithic system with a low SNR (signal to noise ratio), because it is a PN junction photodiode. It also has the problem of difficult viewing in a large field. Therefore, we developed a new radiation sensor, a 2D array PIN photodiodes bump bonded to readout electronics. It has a higher SNR than the CMOS sensor because of an attached intrinsic depletion layer. Moreover, it can adequately accommodate large areas, and sensor thickness because of the use of a Si-wafer from the PIN photodiode process.