Experimental Study On The Photosensitivity Of Topmetal-I Pixel Sensor

Silicon pixel detector, widely used in the field of radiation imaging, has been considered as one of the most common detectors owing to its high spatial resolution, fast readout capability and low cost in high energy physics experiments. Therefore, our pixel laboratory has designed a silicon pixel sensor, named Topmetal-I sensor.The working principle of Topmetal-I sensor is collecting the space charges through the metal window on the top layer of pixel.But it was found that when light irradiated on the pixel, unexpected analog electrical signals ware generated.The aim of this thesis is to explore the sensitivity of Topmetal-I sensor based on this, phenomenon, and then to study its photosensitive mechanism.The main research work includes:To get a photosensitive test platform which can carry out highly precise 2D scan automatically as well as getting and analyzing datum voluntarily, both hardware testing platform along with related controlling and analyzing software should be built. And the functions of this platform include three parts:generating controllable light source, the mastery of precision electric displacement platform coupled with the acquisition and analysis of datum. Moreover, the light source is able to provide the fine facula, the smallest diameter of which can reach to about 100um. The precise electric displacement platform can be programmed, the minimum displacement accuracy of up to 1 um.The data acquisition and analysis system are used to collect and store the analog output signal of the Topmetal-I sensor, and the experimental data are analyzed with the ROOT.Use different laser beams to irradiate Topmetal-I sensor pixels so as to do the photosensitivity measurement. The test consists of two parts:First, scan single-pixel area to detect the photographic properties,at the meantime,we do some measurement to get the relationship between output signals and the light intensity which Topmetal-I sensor accepted in the most light-sensitive area. Then, scan 6*6 pixels array with laser beams, to explore whether the photosensitive characteristics of pixels possess the periodical property.Combining the layout of pixel and the photosensitive characteristics of pixel array,the surmised reason why Topmetal-I sensor is sensitive to light is the photoelectric effect of the NMOS tube on the P epitaxial layer in the source follower and the N trap PMOS tube in the transmission gate.The photographic mechanism has been further demonstrated by observing the expected changes of the output signals when adding the resetting voltage of the top metal under the unchanged light intensity.This thesis discusses the mechanism of the Topmetal-I sensor, which is not only the basis for the elimination of optical signals when Topmetal sensor is used for receiving electrical signals, but also can provide a reference for the design of light sensitive pixel sensor.