Monolithic Active Pixel Sensors (MAPS) Maria Elisabetta Giglio February 3, 2017 Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 1 / 39
Table of contents Introduction 1 Pixel sensors: key to solve complex events Pixel sensors in High Energy Physics (HEP) experiments ALICE Monolithic Pixel Sensor 2 The experiment Upgrade of the Inner Tracking System (ITS) Pixel Chip Technology Read Out Focus on ALPIDE architecture pALPIDE prototype - Test Beam Results 3 π − irradiation Neutron irradiation Conclusions 4 Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 2 / 39
Introduction Outline Introduction 1 Pixel sensors: key to solve complex events Pixel sensors in High Energy Physics (HEP) experiments ALICE Monolithic Pixel Sensor 2 The experiment Upgrade of the Inner Tracking System (ITS) Pixel Chip Technology Read Out Focus on ALPIDE architecture pALPIDE prototype - Test Beam Results 3 π − irradiation Neutron irradiation Conclusions 4 Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 2 / 39
Introduction Pixel sensors: key to solve complex events Silicon sensors Solid state detectors High resolution for particle tracking Principle of operation analogous to gas ionization devices Low ionization energy (3 . 6 eV to create an electron-hole pair) - gas detectors 15-40 eV per electron-ion pair - scintillators 400-1000 eV per photon → Better energy resolution and high signal High density and atomic number - Large energy loss in a short distance → Thinner detectors Figure: Scheme explaining the working principle → Diffusion effect smaller than in gas detectors of a semiconductor as detector. → Higher spatial resolution High carrier mobility → Fast! High intrinsic radiation hardness Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 3 / 39
Introduction Pixel sensors: key to solve complex events Silicon Pixel Sensors 2D-matrix → unambiguous hits High granularity - Small pixel area - Low detector capacitance ( ≈ 1 fF / Pixel ) - Large signal-to-noise ratio (e.g. 150:1) Small pixel volume → low leakage current ( ≈ 1 pA / Pixel ) High cost per surface unit (Large number of readout channels) - Large number of electrical connections - Large power consumption Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 4 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments Pixel detectors - Key to solve complex events L. Musa - CERN (EMMI, GSI 11June, 2015) Si Pixel detectors are high granularity detectors in a harsh environment close to the Interaction Point (IP) Position resolution down to few µ m High track density region → Unambiguous hit info is necessary! High resolution for determination of primary and secondary vertex High interaction rate → fast readout High level of radiation Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 5 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments Pixel sensors - At the heart of the LHC Experiments L. Musa - CERN (Schloss Waldthausen, Germany, August 2016) Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 6 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The variety of pixel technology Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 7 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a CMOS? Complementary Metal Oxide Semiconductors n-channel MOSFET (NMOS) p-channel MOSFET (PMOS) MOSFET= Metal Oxide Semiconductor Field Effect Transistor Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 8 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a MOSFET? (Metal Oxide Semiconductor Field Effect Transistor) Figure: Physical structure of the n-channel enhancement-type transistor. Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 9 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a MOSFET? (Metal Oxide Semiconductor Field Effect Transistor) pn-junctions between substrate and D and S, kept reversed biased V DS is always positive (3-terminal device by connecting B and S) V GS controls the current flow from D to S in the channel region The device is symmetrical respect with S and D Figure: The enhancement-type NMOS transistor with positive voltage applied to the gate. Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 10 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a MOSFET? (Metal Oxide Semiconductor Field Effect Transistor) V GS = 0 2 back-to-back diodes in series between D and S No current conduction from D to S when a V DS is applied (very high resistance ∼ 10 12 Ω) Figure: The enhancement-type NMOS transistor with positive voltage applied to the gate. Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 11 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a MOSFET? (Metal Oxide Semiconductor Field Effect Transistor) V GS > 0 Free holes are repelled from the channel, a carrier-depletion region is formed e − from n+ regions accumulate under the gate, an n-region is created An electric field develop from G and the channel, it controls the amount of charge in the channel (”filed-effect transistor”) Figure: The enhancement-type NMOS V DS makes the current to flow, forming the transistor with positive voltage applied n-channel to the gate. Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 12 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a MOSFET? (Metal Oxide Semiconductor Field Effect Transistor) Threshold voltage V t : V GS such that a sufficient number of e − accumulate to form a conducting channel Overdrive voltage: V OV = V GS − V t → V across the oxide must exceed V t for a channel to form! Figure: The enhancement-type NMOS transistor with positive voltage applied to the gate. Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 13 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a MOSFET? V GS > V t enhances the channel (MOSFET conducts) small V DS : MOSFET as a resistance whose value is controlled by V GS Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 14 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments The CMOS Technology What is a CMOS? Fast switching characteristics → CPUs no ohmic resistors needed → low power easy to implement capacitors Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 15 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments Hybrid Pixel Technology Hybrid Pixel Detector (currently used at LHC) Sensor based on silicon junction detectors Readout chip: ASIC - CMOS sub-micron technology (limited number of producers ∼ 10 world-wide) Sensor and front-end electronics in two separate Si chips and connected by bump bonds (complex and costly) Bump bonds limited to pitches of 30 − 50 µ m (input capacitance, power consumption) Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 16 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments Beyond Hybrid Pixel Detectors... How to design a CMOS particle detector? Monolithic Active Pixel Sensors (MAPS) Monolithic=single process Sensing part incorporated inside the ASIC! (signal processing inside the pixel) → high granularity typical dimensions 20 × 20 µ m 2 Motivation to reduce cost, power, material budget, assembly and integration complexity Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 17 / 39
Introduction Pixel sensors in High Energy Physics (HEP) experiments Monolithic Pixel Sensors in Heavy Ion (HI) experiments L. Musa - CERN (Schloss Waldthausen, Germany, August 2016) Industrial development of CMOS imaging sensors and intensive R&D work within the HEP community! Several HI experiments have selected CMOS pixel sensors for their inner trackers! Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 18 / 39
ALICE Monolithic Pixel Sensor Outline Introduction 1 Pixel sensors: key to solve complex events Pixel sensors in High Energy Physics (HEP) experiments ALICE Monolithic Pixel Sensor 2 The experiment Upgrade of the Inner Tracking System (ITS) Pixel Chip Technology Read Out Focus on ALPIDE architecture pALPIDE prototype - Test Beam Results 3 π − irradiation Neutron irradiation Conclusions 4 Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 18 / 39
ALICE Monolithic Pixel Sensor The experiment The current ALICE detector L. Musa - CERN (EMMI, GSI 11June, 2015) Maria Elisabetta Giglio Monolithic Active Pixel Sensors (MAPS) February 3, 2017 19 / 39
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