Optimization of Tracking Performance of CMOS Monolithic Active Pixel Sensors

Abstract

CMOS Monolithic Active Pixel Sensors (MAPS) provide an attractive solution for high precision tracking of minimum ionizing particles. In these devices, a thin, moderately doped, undepleted silicon layer is used as the active detector volume with the readout electronics implemented on top of it. Recently, a new MAPS prototype was fabricated using the AMS 0.35 m OPTO process, featuring a thick epitaxial layer. A systematic study of tracking performance of that prototype using high-energy particle beam is presented in this work. Noise performance, signal amplitude from minimum ionizing particles, detection efficiency, spurious hit suppression and spatial resolution are shown as a function of the readout pitch and the charge collecting diode size. A test array with a novel readout circuitry was also fabricated and tested. Each pixel circuit consists of a front-end voltage amplifier, capacitively coupled to the charge collecting diode, followed by two analog memory cells. This architecture implements an on-pixel correlated double sampling method, allowing for optimization of integration independently of full frame readout time and strongly reduces the pixel-to-pixel output signal dispersion. First measurements using this structure are also presented.

Pixel circuit optimization for imaging applications using integrated circuit technologies

“…This extra transistor enables Correlated Double Sampling (CDS) [3] [11] [12] to be performed. CDS eliminates kTC noise in a system.…”

“…To reduce the dark current, the operating temperature has to be reduced [3]. The current trend is to develop uncooled detectors mainly due to simpler integration and operating conditions [8].…”

“…For this category, several pixel structures exist. The most commonly used structures are the three-transistor (3T) [2] [3] and the self-biased pixel (SBP) structure [3]. Both structures make use of a source follower and a pixel select transistor.…”

A vertex detector for the International Linear Collider based on CMOS sensors

“…Finding well adapted fabrication processes, which allow integrating the necessary signal conditioning microcircuits in the sensor, with low pixel noise and pixelto-pixel dispersion, is therefore a must. 13 MIMOSA chips have been designed and fabricated exploring 6 different fabrication processes: AMS-0.6µm, AMI- Among them, the AMS 0.35 opto process allowed realizing prototypes (MIMOSA 9 and 11) with the best detection performances [7]. These very satisfactory results were obtained because the noise of the pixels could be kept near 10 e-ENC.…”

Characterization of active pixel sensors in 0.25 /spl mu/m CMOS technology

“…Full CMOS devices using an epitaxial layer as signal charge generation volume were proposed much later [1]- [4]. Currently, an upgrade of the STAR experiment using MIMOSTAR chip developed by IRES is under construction [7], [8], demonstrating that MAPS are a matured technology well suited to build particle detectors.…”