Current-Noise-Power-Spectra for Amorphous Silicon Photodiode Sensors
- PDF / 380,923 Bytes
- 6 Pages / 414.72 x 648 pts Page_size
- 64 Downloads / 239 Views
CURRENT-NOISE-POWER-SPECTRA FOR AMORPHOUS SILICON PHOTODIODE SENSORS J.M. Boudry and L.E. Antonuk Dept. of Radiation Oncology, University of Michigan, Ann Arbor, MI 48109 ABSTRACT Pixelated imaging arrays consisting of hydrogenated amorphous silicon (a-Si:H) photodiode sensors and field effect transistors are under development for x-ray imaging. For such arrays it is important to quantify the sensor noise characteristics as these may, in some cases, limit the array performance for certain applications. The current-noise-power-spectra of -1 pm thick aSi:H p-i-n sensors of various areas are presented. The power spectra were measured for different reverse bias voltages over a frequency range of -0.01 to 1.0 Hz. The power spectra revealed the noise to be composed primarily of flicker noise. The flicker noise showed a 1/fb dependence where b ranged from -1.1 to 1.2. The magnitude of the flicker noise as a function of the sensor leakage current and the sensor area has been investigated and is presented.
INTRODUCTION Photodiode sensors fabricated from hydrogenated amorphous silicon (a-Si:H) are presently being incorporated into two-dimensional, pixelated arrays for applications in x-ray imaging [1]. The role of the a-Si:H sensors in such imaging arrays is to detect the incident x-ray radiation. This detection is performed indirectly by means of an x-ray converter which emits visible light photons when exposed to X rays. The visible light photons are then detected by the sensor which results in the creation of electron-hole pairs. The number of electron-hole pairs created in
a sensor will fluctuate for many reasons, one of which is the random electrical fluctuations, or noise, present in the sensor. A direct consequence of this noise is that the precision to which a sensor can detect an incident x-ray flux may be limited. This could constrain the performance of an array for certain x-ray imaging applications. It is of considerable interest, therefore, to study the electronic noise characteristics of a-Si:H sensors. This paper presents current-noise-power- spectra measurements of a-Si:H photodiode sensors. The sensors studied were designed and fabricated in a manner identical to those incorporated on a-Si:H imaging arrays under development by our group. Consequently, the noise characteristics of these sensors should accurately reflect the noise characteristics of the sensors that comprise an array. Previous power spectra measurements of a-Si:H photodiode sensors ranging in thickness from 5 to 50 tim were reported by Cho et al [2,3]. The present paper concentrates on sensors of -1 im thickness, which is sufficient for visible light detection. Sensors of different areas were examined as a function of reverse-bias voltage. The dependence of the noise on sensor area and leakage current is investigated and explained in terms of Hooge's empirical relation for flicker noise [4,5].
DESCRIPTION OF a-Si:H SENSORS The sensors were fabricated at Xerox PARC using plasma enhanced chemical vapor deposition. Each sensor consists of an u
Data Loading...
