Recent developments on Monolithic Active Pixel Sensors (MAPS) for charged particle tracking. Outline The MAPS sensor (reminder) MIMOSA-22, a fast MAPS-sensor The SUZE-1 FEE chip Random Telegraph Signal and radiation damage Summary and Conclusion Michael Deveaux on behalf of IPHC Strasbourg, IKF Frankfurt/M (Irradiations: F.M. Wagner, MEDAPP, FRM II reactor Munich)

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 2 The operation principle of MAPS Reset +3.3V Output SiO 2 N++ N+ P+ P- P+

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 3 How to build fast MAPS for the MVD: IPHC Strasbourg Sensor array Discriminators On - chip zero suppression Bonding pads + output Amplis. Pixel column Readout bus Expected time resolution: ~10 µs (~100 kFrame/s) MIMOSA-16 and 22 SUZE-1

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 4 Last years status: MIMOSA col. of 128 pixels (25 μm pitch, integrated CDS ) 1 Discriminator/column Tests at CERN-SPS ( 180 GeV pi − ) in Summer 2007 Threshold: 6 mV Detection efficiency: ± 0.05 (stat) % Fake rate: <10 −5 Spatial resolution: 4.6 μm Proof of principle for MAPS with on-pixel CDS and on-chip discriminator (small size only).

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 5 MIMOSA-22, a fast and big chip MIMOSA – 22: Test the MIMOSA-16 concept with higher surface 32 cols x 128 pixels => 128 cols x 576 pixels 17 different (improved) pixels designs: New high gain / low noise pixels Radiation hard pixels Build smaller pixels 18.4 μm instead of 25 µm Read-out time 100 μs ( 10 4 frames/s ) JTAG slow control Programmable test DACs for disciminator tests 40 MHz digital data output Tested with Fe-55 source and CERN 100 GeV/c pion beam

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 6 Test results of the new preaplifyers Noise: 10 < N < 14 e − ENC + 5 e − ENC Fix pattern noise (individual pixel offset) Rad hard: 1e − ENC more than standard version CCE : 3x3 pixels : 70 – 80 % 5x5 pixels : 80 – 90 % Standard SB-Pixel design (Mimosa-16): Successfully used since MIMOSA-4 No dead time Noise: ~15e - with on-pixel CDS, else ~ 9e - New in MIMOSA-22

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 7 Beam test results of MIMOSA-22 Discriminator Threshold All pixels of interest show: Detection efficiency: >99.8% Fake hit rate: O(10 -4 – ) Spatial resolution: ~3.5 µm (~ Pitch / 5) Detection efficiency Fake hit rate

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 8 How to build fast MAPS for the MVD Sensor array Discriminators On - chip zero suppression Bonding pads + output Amplis. Pixel column Readout bus SUZE-1 SUZE – 1 data sparsification circuit Chip with integrated Ø and output memories (no pixels) Algorithm: Step1: find up to 6 series of 4 neighbour pixels / raw in block of 64 cols. Step2: Read-out all blocks, keep up to 9 series of 4 pixels. Output memory: 4 x (512x16 bits) taken from AMS I.P. lib. Surface: 3.9 × 3.6 mm² Test result: Works fine up to 115% clock frequency Can handle up to 100 hits/frame at 10 4 frame/s

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 9 Next Step: MIMOSA-26 MIMOSA-22 Sensor SUZE-1 Ø -suppression circuit MIMOSA-26 Pixels + Ø-suppression Expanded surface: 1152 cols x 576 pixels 21.2 x 10.6 mm² 18.6 µm pixel pitch Expanded data sparsification circuit 18 blocks of 64 columns Max. 9 clusters per row Data rate: 80 Mbits/s Submission November 2008

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 10 Radiation hardness studies together with

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 11 Random Telegraph Signal Signal [ADC] Time Random Telegraph Signal: Modulation of an output signal between two “quantum levels”. Random period length. RTS in MAPS sensors first described by Hopkinson (2000) * Output signal of two MAPS pixels RTS may generate fake-hits if amplitude exceeds discriminator threshold. Problem for MAPS being used in HEP – experiments? D. Doering, Bachelor Thesis * G.R. Hopkinson: “Radiation Effects in a CMOS Active Pixel Sensor”, IEEE-NSS Vol. 47, No. 6, P. 2480

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 12 Fake hit rate of MAPS with Random Telegraph Signal Affected SB-pixels remain sensitiv. The fake hit rate of MAPS shrinks with cooling. Identified RTS pixels contribute ~60 – 80 % of all fake hits. MIMOSA-18 (SB-pixel, irradiated at MEDAPP, FRM II, Munich) Preliminary D. Doering, Bachelor Thesis

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 13 Distribution of RTS-pixels D. Doering, Bachelor Thesis Pixel X Pixel Y Normal Pixel RTS Pixel Up to ~10% of all pixels are affected. Masking of pixels is not possible but pixels stay sensitiv  Operate pixels, tolerate fake hits ( ~ 10 4 / frame for full MVD) Note: Fast MAPS might show less RTS than MIMOSA-18

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 14 Sensors with improved charge collection efficiency MIMOSA-Pixel with 10 x 10 µm² Standard collection diode ( ~ 3 x 4 µm²)

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 15 Sensors with improved charge collection efficiency How to escape here? Bigger collection diodes may improve CCE Improved CCE => improved radiation hardness Tested with MIMOSA-19 (by IPHC) Diode 1Diode 2

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 16 Results A. Büdenbender, Bachelor Thesis Charge collection efficiency is indeed substantially increased But the bigger collection diodes generate more noise T= -20 °C

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 17 S/N of the sensors A. Büdenbender, Bachelor Thesis Both MIMOSA-18 and MIMOSA-19 seem fairly radiation hard Big diodes have no advantages because of high noise Insufficient S/N

M. Deveaux, 12th CBM Collaboration Meeting, Oct JINR Dubna, Russia 18 Summary At IPHC, a first sizable chip with column parallel readout was produced and tested in the CERN – SPS pion beam: Features: reduced noise 15 e - => 10 – 14 e -, det. eff. > 99.8 % pitch 18.4 μm, resolution = 3.5 µm An FEE chip with cluster finding circuits (SUZE-1) was successfully tested. MIMOSA-26 integrating the full discrimination chain will be submitted in November. Radiation hardness tests were undertaken at IKF: A radiation hardness of n eq /cm² has been shown for two pixel concepts The effect of Random Telegraph Signal was identified as dominating source of background hits in MAPS Studies on RTS suggest, that RTS can be tolerated if chips are cooled