Radiation tolerance of MAPS M. Deveaux1 on behalf of IKF Frankfurt and the IPHC-PICSEL group 1Institut für Kernphysik, Goethe Universität Frankfurt am Main

Non-ionizing radiation damage Ionizing radiation damage Outline Definitions Non-ionizing radiation damage Ionizing radiation damage Annealing effects Random Telegraph Signal M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Ionizing and non-ionizing radiation To be measured and improved: Radiation hardness against… Ionising radiation: Energy deposited into the electron cloud May ionise atoms and destroy molecules Caused by charged particles and photons Non-ionising radiation: Energy deposited into the crystal lattice Atoms get displaced Caused by heavy (fast leptons, hadrons) charged and neutral particles M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

The operation principle of MAPS +3.3V Reset +3.3V Output SiO2 SiO2 SiO2 N++ N++ N+ P+ P- P+ M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Tolerance against non-ionising radiation +3.3V Output +3.3V GND SiO2 SiO2 GND SiO2 SiO2 N+ P++ P++ N++ P++ Bulk damage M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile Non-ionising radiation Energy deposit into crystal lattice

Tolerance against non-ionising radiation +3.3V Output +3.3V GND SiO2 SiO2 GND SiO2 SiO2 N+ P++ P++ N++ P++ M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

CCE-Measurements with 55Fe 5,9 keV (55Fe) Photons: Small, point-like interaction region. Number of generated e/h pairs similar to MIPS 5,9keV=>1640 e/h pairs Which fraction of electrons is collected? => Charge collection efficiency (CCE) M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

How to study charge collection efficiency (in groups of 4 pixels) After neutron irradiation Before neutron irradiation Hits in Epitaxial-Layer Hits in Diode M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile 8

CCE as function of neutron fluence Charge collected in groups of 4 pixels CCE decreases with increasing radiation. Decrease is slower for thin epi-layers, high diode density, big diodes M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Tolerance against non-ionising radiation +3.3V Output +3.3V GND SiO2 SiO2 GND SiO2 SiO2 N+ P++ P++ N++ P++ M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Tolerance against non-ionising radiation Mi-18 Mi-15 Mi-9 Mi-9 Small pixels seem mandatory to improve radiation hardness But: Need to readout additional pixels => Reduced speed, higher power etc… M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Tolerance against non-ionising radiation +3.3V Output +3.3V GND SiO2 SiO2 GND SiO2 SiO2 N+ P++ P++ N++ P++ E Electric field increases the radiation hardness of the sensor Draw back: Need CMOS-processes with low doping epitaxial layer M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

CCE of MIMOSA-26, standard vs. high resistivity Radiation dose CCE shrinks after irradiation to <50% of initial value. x 1012 n/cm² -20°C, Std. epi, seed pixel CCE remains mostly stable. -20°C 400 Ohm cm, 15µm , seed pixel D. Doering M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Radiation tolerance Sensor: - Mi-18 AHR, SB-Pixel, 10 µm pitch 3 · 1014neq/cm² + O(3 MRad) Not irradiated Sensor: - Mi-18 AHR, SB-Pixel, 10 µm pitch - Epitaxial layer: 400 W cm, 15 µm Irradiation: - fast reactor neutrons (Triga, Ljubljana) - Chip not powered during irradiation - Dose: 3 · 1014neq/cm² + O(3 MRad) Noise increases Noise increases => Compensate with cooling. <20% less entries Thinner active vol.? CCE ok Gain ok Fe-55 (X-rays) Ru-106 (b-rays) 99% det. eff. after irrad. 620e (MPV) 490e (MPV) <20% less signal Thinner act. vol.? Preliminary conclusion: Sensor tolerates 3 · 1014neq/cm², to be confirmed in beam test

Radiation tolerance of MIMOSA-HR Preliminary T< -30°C! M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Leakage current, an illustrative example 1013neq/cm² Leakage current: M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Dependencies of (shot-)noise 1 8 ms 10 80 -25°C +10°C +40°C MIMOSA-11, 500kRad X-rays Dose [neq/cm²] Noise [e ENC] too high Mi18, A. Büdenbender, Bachelor Thesis still ok 2e13 50 Radiation induced noise is reduced by: Cooling Fast readout M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Ionizing radiation Ionising radiation: Energy deposited into the electron cloud May ionise atoms and destroy molecules Caused by charged particles and photons M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Response of MAPS to 55Fe-photons before and after irradiation Signal of MIMOSA-2 before and after 400kRad Design and test of 6 detector generations was needed to learn and improve the design: MIMOSA-2 MIMOSA-4 SUCCESSOR-1 SUCCESSOR-2 MIMOSA-9 MIMOSA-11 Dead after 400 kRad M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Radiation tolerance against ionising radiation Results +3.3V Reset +3.3V Output SiO2 SiO2 Positive Charge N++ N++ N+ P+ P- P+ M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile Ionising radiation Energy deposit into electron cloud

Improvement of radiation tolerance Output SiO2 N++ N+ P++ GND P++ guard ring cuts conduction paths Thicker P+ isolation found in AMS 0.35 M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Dependencies of (shot-)noise 1 8 ms 10 80 -25°C +10°C +40°C MIMOSA-11, 500kRad X-rays Radiation induced noise is reduced by: Cooling Fast readout M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

How to improve radiation hardness MIMOSA-2 before and after 400kRad OK after 1000 kRad Open issue: Radiation tolerance of “column parallel sensors” M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Column parallel sensors M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Radiation tolerance of column parallel sensors M. Koziel M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

“Single weak point” was not spotted => Use 0.18 µm – process. M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Pedestals in an 1 MRad irradiated Mimosa-26 After 1 day After 4 days After 19 days After 31 days tint = 400µs (fclk = 20MHz), Tcooling = 15°C Origin of the effect not yet understood. Effect substantially alleviated at nominal readout frequency. Currently radiation tolerance to ~300 kRad M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

About the benefits of a little fever Thermal annealing About the benefits of a little fever M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Annealing: Modify defects by thermal treatment Beneficial annealing: Radiation damage is reduced Reverse annealing: Additional damage is observed (defects group to more dangerous defect clusters) Used chips: Mimosa19 73k pixels; 12 µm pixel pitch Read out time: 3.69 ms (only analog read-out) a) ~10 keV X-rays (200 kRad) b) Fast reactor neutrons: +(~100 kRad γ) → ionizing radiation suppressed (sensors not powered) c) Combined radiation: → ; 1 year at room temperature ; 200 kRad X-rays. M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Annealing study, temperature profile Time Neutron radiation 1 year X-ray Measurements and storage at +20°C (280h) Heating at +80°C (73h) Measurements and storage at +20°C (191h) 2h transport T[°C] +80°C +20°C M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Annealing study, results D. Doering, RESMDD 2011 Annealing at +20°C neglected No reverse annealing observed for up to 70h at +80°C. M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Annealing of noise Noise at -20°C (combined radiation/no annealing at +80°C) M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Random Telegraph Signal M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Excotic effects: Random Telegraph Signal Fake hits in MIMOSA-18 (Window of 64x64 pixels) After 1013 neq/cm² Fake hits in 5000 Events D. Doering, Bachelor Thesis PixelNr. M. Deveaux, Seminar at IPHC 13.01.09,  Strasbourg, France

Random Telegraph Signal, a radiation damage of MAPS UCDS [ADC] Time Output signal of two MAPS pixels U1 Q IL Threshold Irradiate sensor with ~ 1 MeV reactor neutrons (MedApp @ FRM II, Garching) Observation: RTS may generate many fake hits >> 1% of all pixels generate fake hits How to improve? What is the origin? Working hypothesis: IL(t) is modulated=> RTS in diode. M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Temperature effects on RTS Hopkins et al. (2000): Frequency and amplitude of RTS increase with temperature Output signal of a selected MAPS pixel showing RTS * G.R. Hopkinson: “Radiation Effects in a CMOS Active Pixel Sensor”, IEEE-TNS Vol. 47, No. 6, P. 2480 Hypothesis: Cooling => RTS-Amplitude < Threshold => No fake hits? M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Identified RTS - pixels as function of temperature (3T-pixel) RTS pixel if signature with: Amplitude >150e ENC Tmin = ~ 0.5s Tmax= ~ 45 min Preliminary Number of identified RTS - pixels is dramatically reduced by cooling M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Fake hit rates of irradiated MAPS detectors Identified RTS provides 60-80 % of all fake hits Fake hit rate of warm 3T-pixels seems inacceptable Cooled SB-pixels show acceptable fake hit rate for < 1013 neq /cm² M. Deveaux, Seminar at IPHC 13.01.09,  Strasbourg, France

Summary and conclusion MAPS react to non-ionizing radiation with: Increased leakage current Increased noise Random Telegraph Signal Alleviate with cooling and fast readout Drop in charge collection efficiency Alleviate with small pixels, high resistivity epitaxial layer Limits: Some 1012 neq/cm² (room temperature), potentially > 1014 neq/cm² (if cooled). Ionizing radiation: Strongly increased leakage currents and noise Pedestal shifts “odd effects” Alleviate with cooling and faster readout Use 0.18µm process for future improvement Limits: ~ 300kRad (Col || readout, room temperature), > 1 MRad (analog readout, cooled) M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Backup Backup M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Radiation tolerance Sensor: - Mi-18 AHR, SB-Pixel, 10 µm pitch 3 · 1014neq/cm² + O(3 MRad) Not irradiated Sensor: - Mi-18 AHR, SB-Pixel, 10 µm pitch - Epitaxial layer: 400 W cm, 15 µm Irradiation: - fast reactor neutrons (Triga, Ljubljana) - Chip not powered during irradiation - Dose: 3 · 1014neq/cm² + O(3 MRad) Noise increases Noise increases => Compensate with cooling. <20% less entries Thinner active vol.? CCE ok Gain ok Fe-55 (X-rays) Ru-106 (b-rays) 99% det. eff. after irrad. 620e (MPV) 490e (MPV) <20% less signal Thinner act. vol.? Preliminary conclusion: Sensor tolerates 3 · 1014neq/cm², to be confirmed in beam test

Chips with intrinsic leakage current compensation (SB-pixel) IL t vdd (+3.3V) IC U2 IC, U2 t IL U1 UCDS t Threshold (Output) RTS should only be visible in UCDS, if new equilibrium is being established Steps should be visible in U2 M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Raw data from SB-pixels with RTS Uvdd-U2 U1(t) [shifted, a.u.] UCDS (t) [a.u.] UCDS Step within the lifetime of the readout system Steps within dead time of the readout system Time [a.u.] Observation: SB-pixels suppress RTS in output signal. M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Temperature measurement T of sensor T of cooling liquid -3°C (-20°C) 44 M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

on-line compilation: http://sesam.desy.de/~gunnar/Si-dfuncs Relative non ionising dose of neutrons and pions Data from: A. Vasilescu and G. Lindstroem, Displacement damage in Silicon on-line compilation: http://sesam.desy.de/~gunnar/Si-dfuncs M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile

Need for high resistivity Size of the depleted zone Doping concentration Idea: Decreasing the doping concentration from 1015 to 1013 should increase the size of the depleted zone. Manifacuring processes became only recently available Sensors: MIMOSA-26 AHR (low depletion voltage, full readout chain) MIMOSA-18 AHR (high depletion voltage, analog readout) M. Deveaux, Workshop on integrating highly granular and light vertex detectors , 6-9th Sept. 2011, Mont Saint Odile