FSBB-M and FSBB-A: Two Large Scale CMOS Pixel Sensors Building Blocks Developed for the Upgrade of the Inner Tracking System of the ALICE Experiment Frédéric Morel (on behalf of PICSEL team of IPHC Strasbourg) Outline  Starting point: STAR-PXL  MISTRAL and ASTRAL  Description  Test results  Conclusions

Starting point: Ultimate chip in STAR TWEPP 2014IPHC Physics data taking from March to June 2014 MIMOSA28 (ULTIMATE) Pictures Credit: Berkley Lab and IPHC

Towards Higher Read-Out Speed and Radiation Tolerance Requirements for inner and outer barrel (compared to STAR-PXL): Main improvements required while remaining inside the virtuous circle of spatial resolution, speed, material budget, radiation tolerance  move to 0.18 µm process  To enhance the radiation tolerance High resistivity epitaxial layer Smaller feature size process  To accelerate the readout speed More parallelised read-out Optimised number of pixels per column New pixel array architectures Smaller feature size process Tight schedule (production in 2016) and large surface (10 m²)  2 readout architectures R&D in parallel Synchronous readout: mature and robust architecture (MIMOSA28 like) Asynchronous readout: new and challenging architecture TWEPP 2014IPHC t r.o.  sp TIDFluenceT op PowerActive Area STAR-PXL<~ 200 µs < 4 µm150 kRad3x10 12 n eq /cm² 30 °C160 mW/cm²0.15 m² ITS-in<~30 µs<~ 5 µm700 kRad10 13 n eq /cm²30 °C< 300 mW/cm²0.17 m² ITS-out<~30 µs<~ 10 µm15 kRad4x10 11 n eq /cm² 30 °C< 100 mW/cm²~ 10 m²

Sensors R&D for the upgrade of the ITS: Our Strategy TWEPP 2014IPHC R&D of up- & down-stream of sensors performed in parallel at IPHC in order to match the ITS timescale for 2 final sensors (~3x1.3 cm²) - Mature architecture: MISTRAL = MIMOSA Sensor for the inner TRacker of ALICE Relatively moderate readout speed (200 ns/ 2rows)  ~ 200 mW/cm², σ sp ~ 5 µm for inner layers  ~ 100 mW/cm², σ sp ~ 10 µm for outer layers - Improved architecture: ASTRAL = AROM Sensor for the inner TRacker of ALICE Higher speed (100 ns/ 2rows) + Lower power  ~ 85 mW/cm², σ sp ~ 5 µm for inner layers Modular design + reused parts  optimising R&D time  FSBB-M (Full Scale Building Block) : 1/3 of MISTRAL final sensor  FSBB-A (Full Scale Building Block) : 1/3 of ASTRAL final sensor Alternative sensor with asynchronous readout: ALPIDE  Ref: Ping PIXEL 2014 UpstreamDownstream

Power density, Integration time and Spatial resolution MISTRAL for outer layers:  Sensitive area ( 3 x 1.3 ) cm²  1 SUZE per final sensor  N Col = No. of Columns (modulo 32)  N FSBB = No. of FSBBs per final sensor  N Col /N FSBB = No. of rows  Pitch Row = µm / (N Col /N FSBB )  Pitch col = µm / N Col Pixel pitches vs Spatial resolution (  sp )   sp = 7 [Pitch col x Pitch row )/(22 x 66) ] k µm with k = ½ or 1  Empirical formula for a specific tech- nology and architecture based on the spatial resolution of tested chip with a pixel area of 22 x 66 µm² No. of Rows vs Readout time (T RO )  T RO = 200 x (N Col / N FSBB ) / 2 ns No. of columns vs Power density (PD)  PD = P / area  P = (0.117 x N Col x 2) x x N Col / 32 mW  P opt = (0.09 x N Col x 2) x x N Col / 32 mW TWEPP 2014IPHC

Upstream of MISTRAL Sensor TWEPP 2014IPHC Pixel optimisation:  Sensing node: N well -P EPI diode Optimisation = f (diode size, shape, No. of diodes/pixel, pixel pitch, EPI) No accurate model exists  need submission iterations  In-pixel amplification and cDS: Limited dynamic range (supply 1.8 V) compared to the previous process (3.3 V) Noise optimisation especially against random telegraph signal (RTS) noise  Sensing diode: avoid STI around N-well diode  RO circuit: avoid using minimum dimensions for key MOS & avoid STI interface  Trade off between diode size, input MOS size w.r.t. S/N before and after irradiation Beam test of MIMOSA-22THRa  Detection efficiency ≥ 99.8% while Fake hit rate ≤ O(10 −5 )  22×33 μm² binary pixel resolution: ~5 µm as expected from former studies  Final ionisation radiation tolerance assessment under way Designed by Y. Degerli (Irfu/AIDA) Layout of 2 discri. (1 columns) ~300 µm Pixel levelColumn level MIMOSA-34 Sensing node opt. MIMOSA-32FEE Amp opt. MIMOSA-32N RTS opt. MIMOSA-22THRa1&2 Chain opt. => 1 D/col MIMOSA-22THRb Chain opt. => 2 D/col 2 x FSBB_M0 Verify full chain and full functionalities 1.6 cm 1.8 cm

Test Results of FSBB-M Transfer function measurement:  208 discriminators connected to 80,000 pixels  SUZE activated normally  pure noise measurement performed in obscurity Perturbations due to cross-talk with modest impact on TN & FPN  Submission of a corrected version next month TWEPP 2014IPHC TN & FPN for 17 different chips ThresholdFake rate 4 mV mV mV mV mV FPN in transfer function mode FPN in detection mode TN ~ 0.87 mVFPN ~ 0.55 mV

TWEPP 2014IPHC Upstream of ASTRAL sensor Thanks to the quadruple-well technology, discriminator integrated inside each pixel  Analogue buffer driving the long distance column line is no longer needed Static current consumption reduced from ~120 µA up to ~14 µA per pixel  Readout time per row can be halved down to 100 ns (still with 2 rows at once) due to small local parasitics Sensing node & in-pixel pre-amplification as in MISTRAL sensors In-pixel discrimination  Topology selected among 3 topologies implemented in the 1st prototype AROM-0  Several optimisations on the 2 most promising topologies in AROM-1 AROM-0 AROM-1 FSBB_A0 1/3 of final sensor 1.6 cm 0.9 cm

Test Results of the Upstream Part of ASTRAL Sensor Preliminary lab test 30 °C 100 MHz (instead of 160 MHz)  Current acquisition board limitation AROM-1b/c  Discri alone: TN ~ 0.75 mV, FPN ~ 0.63mV  Discri+pixel: TN ~ 1.1 mV, FPN ~ 0.66mV AROM-1e tests are ongoing  Discri alone: TN ~ 0.29 mV, FPN ~ 0.19mV  Discri+pixel: TN ~ 0.94 mV, FPN ~ 0.23mV TWEPP 2014IPHC AROM-1e optimisation is validated Some residual coupling effects are investigated

Summary TWEPP 2014IPHC MISTRAL: architecture validated  FSBB-M: Spatial resolution (22x33 µm² pixel) ~5 µm Integration time ~40 µs Power consumption ~200 mW/cm² Detection efficiency <~ 100 % for fake hit rate ≤ O(10 −5 ) (beam test of FSBB-M in Oct./Nov.) Yield: 25 chips operational among 25 chips tested  MISTRAL for outer layers to be submitted in Q2/2015: Spatial resolution (36x62.5 µm² pixel) ~10 µm expected Integration time ~20 µs Power consumption ~100 mW/cm² ASTRAL: architecture validation on going  ASTRAL pixel front-end amplification (same as in MISTRAL) validation completed  Downstream of ASTRAL (shares the same logic with MISTRAL) validation completed  In-pixel discrimination validation completed  ASTRAL exhibits 2 x faster readout and lower power consumption than MISTRAL Integration time: <~20 µs Power consumption ~85 mW/cm² for inner layers

Conclusions TWEPP 2014IPHC ALICE-ITS sets a new challenge in pixelated devices  Large detector areas may be equipped with granular and thin pixels (at affordable cost) 3 complementary sensor architectures developed  1st full scale prototypes fabricated in Spring ’14  1st test results MISTRAL : rolling shutter, directly derived from the STAR-PXL sensor  mature & robust ASTRAL : rolling shutter approach pushed towards its limits with in-pixel discrimination ALPIDE : asynchronous (like hybrid pixels), most challenging but highest potential  All 3 seem operational but their performance assessment is still under way Further optimisation of design parameters on-going Design finalisation in 2015  production in 2016 High potential 0.18 μm CIS process for HEP experiment  Feature size, deep P-well, 6 ML, ”thick” and high-resistivity epitaxy, large reticule New step in particle detection performances with CPS w.r.t STAR-PXL pioneering device  Still room for improvement towards real potential of CPS: smaller feature size, more ML, etc. New horizons to develop high potential CPS to reach sub-microsecond integration time, ultra low power (few tens of mW/cm²), and high radiation tolerance.

TWEPP 2014IPHC Thank You !