A novel Monolithic Active Pixel Sensor (MAPS) for charged particle tracking made in a standard CMOS technology is proposed. The sensor is a photodiode, which is readily available in a CMOS technology. The diode has a special structure, which allows the high detection efficiency required for tracking applications. The partially depleted thin epitaxial silicon layer is used as a sensitive detector volume. Semiconductor device simulation, using either ToSCA based or 3-D ISE-TCAD software packages shows that the charge collection is efficient, reasonably fast (order of 100 ns), and the charge spreading limited to a few pixels only. A first prototype has been designed, fabricated and tested. It is made of four arrays each containing 64×64 pixels, with a readout pitch of 20 μm in both directions. The device is fabricated using standard submicron 0.6 μm CMOS process, which features twin-tub implanted in a p-type epitaxial layer, a characteristic common to many modern CMOS VLSI processes. Extensive tests made with soft X-ray source ( 55 Fe) and minimum ionising particles (15 GeV/ c pions) fully demonstrate the predicted performances, with the individual pixel noise (ENC) below 20 electrons and the Signal-to-Noise ratio for both 5.9 keV X-rays and Minimum Ionising Particles (MIP) of the order of 30. This novel device opens new perspectives in high-precision vertex detectors in Particle Physics experiments, as well as in other application, like low-energy beta particle imaging, visible light single photon imaging (using the Hybrid Photon Detector approach) and high-precision slow neutron imaging.

A monolithic active pixel sensor for charged particle tracking and imaging using standard VLSI CMOS technology

Active pixel sensor array as a detector for electron microscopy.

A monolithic active pixel sensor (MAPS) for charged particle tracking based on a novel detector structure was proposed, simulated, fabricated and tested. The detector designed accordingly to this idea is inseparable from the readout electronics, since both of them are integrated onto the same, standard for a CMOS process, low-resistivity silicon wafer. The individual pixel is comprised of only 3 MOS transistors and a photodiode collecting the charge created in a thin undepleted epitaxial layer. This approach provides the whole detector surface sensitive to radiation (100% fill factor) with reduced pixel pitch(very high spatial resolution). This yields a low cost, high resolution and thin detecting device. The detailed device simulations using an ISE-TCAD package have been carried out in order to study a charge collection mechanism and to validate the proposed idea. Consequently, two prototype chips have been fabricated using 0.6 /spl mu/m and 0.35 /spl mu/m CMOS processes. Special radiation tolerant layout techniques were used in the second chip design. Both chips were tested and fully characterised. The pixel conversion gain was calibrated using 5.9 keV photons and prototype devices were exposed to the 120 GeV/c pion beams at CERN. Obtained results preceded by general design ideas and simulation results are reviewed.

http://epp.fnal.gov/DocDB/0002/000251/001/Monolithic_Pixel_.pdf

Design and testing of monolithic active pixel sensors for charged particle tracking

Monolithic active pixel sensors introduce a detection technique, where the active detecting element is a thin, moderately doped, and undepleted silicon layer and the readout electronics is implanted on top of it. The built-in potential, resulting from differences in doping, screens both parts, as well as it confines the charge diffusing to the readout electrodes. The R&D was triggered by the increasing need of high performance flavour identification capabilities that should be provided by future vertex detectors. The viability of the technology and its high tracking performances were demonstrated with small-scale prototypes, made of small arrays of a few thousands of pixels and more recently with a first prototype of a serviceable size of one million pixels. This paper summarizes results from tests performed with relativistic charged particles on prototypes essentially fabricated with a classical 3-transistor pixel configuration. Within the last year, two novel ideas optimising the pixel design for a vertex detector have been developed. They are presented with test results assessing their suitability.

Development of monolithic active pixel sensors for charged particle tracking

Direct electron imaging in electron microscopy with monolithic active pixel sensors

A novel monolithic active pixel sensor for charged particle tracking has been designed and fabricated in a standard CMOS technology. The device architecture is identical to a CMOS camera, recently being proposed as an alternative to CCD sensors for visible light imaging. The partially depleted thin epitaxial silicon layer is used as a sensitive detector volume. The sensor is a photodiode having a special structure, which allows the high detection efficiency required for tracking applications A first prototype was made of four arrays each containing 64×64 pixels, with a readout pitch of 20 μm in both directions. An architecture allowing serial readout of the analogue information from each pixel has been implemented. To evaluate the tracking performance of such a device, series of tests have been performed using a high-energy particle beam. A detailed analysis of the beam test data presented in this work demonstrate close to 100% minimum ionising particle detection efficiency and a good enough signal-to-noise ratio of more than 30.

Particle tracking using CMOS monolithic active pixel sensor

A novel technique for detecting minimum ionising particles (i.e. m.i.p.) was designed and a first prototype fabricated in a standard CMOS technology, guided by very high vertex detector performances required in future collider experiments. The device architecture resembles CMOS cameras, a recent alternative to CCD sensors for visible light imaging. The performance of the first prototype was evaluated with high energy π − beams at CERN. Preliminary test results demonstrate that the sensors detect m.i.p.s with very high efficiency and signal-to-noise ratio and provide excellent surface resolution.

Monolithic active pixel sensors for a linear collider

A novel Monolithic Active Pixel Sensor (MAPS) for charged particle tracking is presented. The partially depleted thin epitaxial layer of a low-resistivity silicon wafer is used as a sensitive detector volume from which the charge liberated by ionising particles is collected by diffusion. The sensor is a photodiode within a special structure allowing the high detection efficiency required for tracking applications. Two prototypes have been designed and fabricated using standard 0.6 and 0.35micron CMOS processes. Results of the first prototype are presented, which is made of four arrays, each containing 64×64 pixels with a readout pitch of 20 microns in both directions. Extensive tests made with a soft X-ray source (Fe) and beams of minimum ionising particles (pions of 15 and 120 GeV/c) at CERN have demonstrated the predicted performance. The individual pixel noise of around 12 ENC leads to an extremely favourable signal to noise ratio for minimum ionising particles for which over 1000 electrons can be collected at the peak of the Landau distribution. The new circuit in the 0.35-micron process on a thinner epitaxial layer seems to have similar good performance. These new devices are extremely promising for future high precision vertex detectors as they provide solutions with a very low material budget and with high resolution at relatively low cost due to their fabrication in a standard submicron CMOS technology.

/pdf/monolithic-active-pixel-sensors-for-high-resolution-vertex-vxsn2bvvh2.pdf

G. Orazi

Papers

Design and testing of monolithic active pixel sensors for charged particle tracking

Particle tracking using CMOS monolithic active pixel sensor

Monolithic active pixel sensors for a linear collider

Particle tracking using CMOS monolithic active pixel sensor

Monolithic active pixel sensors for high resolution vertex detectors