Radiation damage in silicon sensors Overview radiation damage due to heavy particles State-of-the-Art sensors In case of any questions: Jaap.Velthuis@bristol.ac.uk Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) sLHC radiation dose 5 year radiation dose close to beam pipe ~1016 neq/cm2 too high for state-of-the-art standard silicon sensors Jaap Velthuis (University of Bristol)

Radiation with protons/neutrons Energetic radiation knocks atoms out of lattice: similar to doping Energy needed to displace atom from lattice=15eV This damage is called Non-Ionizing Energy Loss (NIEL) Displacement changes band structure Donor removal Acceptor generation Jaap Velthuis (University of Bristol)

Radiation damage: Leakage current I = Volume Material independent linked to defect clusters Scales with NIEL Temp dependence Thermal runaway  = 3.99  0.03 x 10-17Acm-1 after 80minutes annealing at 60C Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) Type inversion Dopants may be captured into defect complexes. Donor removal and acceptor generation type inversion: n  p depletion width grows from n+ contact Increase in full depletion voltage P-strips in p-bulk = 0.025cm-1 measured after beneficial anneal Jaap Velthuis (University of Bristol)

Partially depleted detectors undepleted Depletion zone grows from p-n-junction. Need depleted area around strips for isolation Signal proportional depleted area Undepleted region like high-ohmic resistor If detector partially depleted from strip side  only charge in depleted region contributes  smaller signal, similar spatial resolution from backplane carriers travel towards strips, but don’t reach it signal spread over many strips poor spatial resolution undepleted Jaap Velthuis (University of Bristol)

Solutions radiation damage N+-on-n detectors (LHCb) Need full depletion before type inversion After radiation p-type bulk P-type bulk sensors Just becomes more p-type Cool to cryogenic temperatures No trapping, no leakage current Diamond sensors Very high bandgap: no background Very though lattice Jaap Velthuis (University of Bristol)

Solutions radiation damage Oxygenation Oxygen binds and neutralises vacancies Czochralski silicon “cheap” Si, contains loads of oxygen no type inversion  donor generation overcompensates acceptor generation 3D sensors Spacing electrodes so small: full depletion at very low voltages “Edgeless” Jaap Velthuis (University of Bristol)

State-of-the-Art devices DEPFETs Very thin p-n sensor with in-pixel amplification ISIS Pixel sensor with short CCD each pixel MAPS 3d integrated devices Trend is towards thin, fast and integration Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) DEPFET Principle ~1µm p+ n+ rear contact drain bulk source p s y m e t r a x i n internal gate top gate clear - + 50 µm MIP Was developed towards ILC, so needs to be very thin and fast Will be used at SuperBelle A p-FET transistor (=amplification!) integrated in every pixel. By sidewards depletion potential minimum created below internal gate. Electrons, collected at internal gate, modulate transistor current Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) DEPFET Principle (II) Advantages: Fast signal collection due to fully depleted bulk Low noise due to small capacitance and amplification in pixel Transistor can be switched off by external gate – charge collection is then still active ! Non-destructive readout Disadvantages: Need to clear internal gate. Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) Ladder proposal Detectors 50µm thick, with 300µm thick frame yields 0.11% X0 SWITCHER & CURO chips connected by bump bonding Radiation hardness not an issue: can change operating voltage to correct Vthres shift CURO SWITCHER Jaap Velthuis (University of Bristol)

Thinning first ‘dummy’ samples: 50µm silicon with 350µm frame sensor wafer handle wafer 1. implant backside on sensor wafer 2. bond wafers with SiO2 in between 3. thin sensor side to desired thick. 4. process DEPFETs on top side 5. etch backside up to oxide/implant first ‘dummy’ samples: 50µm silicon with 350µm frame thinned diode structures: leakage current: <1nA /cm2 Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) Testbeam results Placed 450µm thick DEPFET in testbeam Cluster signal (5σ seed, 2σ neighbour cut) S/N=112.0±0.3 for 450 μm  S/N≈12 for 50 μm Position resolution 1.82µm (incl telescope error) for 22µm pitch Intrinsic resolution 1.25μm Second best ever measured! Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) ISIS Operational Principles: Every pixel has mini CCD to store charge: burst camera with multiframes Charge collected at photogate Transferred to storage pixel during bunch train 20 transfers per 1ms bunch train Readout during 200ms quiet period after bunch train Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) ISIS It works! Here you see Fe55 spectrum Results of a laser scan And position resolution in a beam test ISIS2 is currently available preliminary Using η preliminary Jaap Velthuis (University of Bristol)

MAPS operation principle Epitaxial layer forms sensitive volume (2-20m) Charge collection by diffusion (no field!) Charge collected by N-well Build amplifiers in P-well (Intrinsic amplification) Only NMOS possible Small signals (~800e-), but small noise (~15e-) Developed for: SuperBelle, STAR vertex detector, replacing CCDs in camera’s & satellites Vreset Vdd Out Select Reset Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) MAPS (dis)advantages Advantages: Integrated detector and electronics High S/N (first amplification in pixel) Possible in-pixel or on-chip intelligence (System on chip) Low power consumption Radiation hardness (w.r.t. CCDs) Small pixel size (10-20 m) Thin can be less than 20 m 50µm in industry Standard CMOS  “cheap” Room temperature operation Excellent position resolution Disadvantages: Thin active volume  low signals (80 eh pairs /µm) Smaller CMOS sizes usually yield thinner epilayer thickness Jaap Velthuis (University of Bristol)

On chip data processing: MIMOSA VIII TSMC 0.25 µm (8 µm epitaxial layer) 32//columns of 128 pixels 25x25 µm2 pixels On-pixel CDS Discriminator on each column 55Fe Jaap Velthuis (University of Bristol)

MAPS with storage: FAPS Active pixel with memory cells: sample and store charge during bunchtrain  can be read out in 200 ms in between trains  no high speed readout required! FAPS: 10 memory cells in each pixel First step of incorporating in-pixel intelligence S/Ncell between 14.7±0.4 and 17.0±0.3 Issue: need 20 C’s per pixel. Small pixels  small C’s. Then spread in actual C-values large. Bad for S/N. Seed 3x3 5x5 FAPS Column Output Write amplifier RST_W SEL A 1 Memory Cell #0 Memory Cell #1 Memory Cell #9 Ibias Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) MAPS Problem with MAPS: charge collection by n-well. So can only make p-mos transistors and electronics. Now trying to do proper CMOS in-pixel using deep p-well Plan to incorporate signal processing logic inside the pixels! Store X and Y location (14μm res. in X and Y) Digitize seed signal with 5bit ADC Get 13 bit time stamp Sum lower signals for total cluster charge Use higher threshold for hit flag Per strixel only one 32 bit output word/train Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) 3D integrated devices New development in electronics industry Put memory directly on processor Reduces R, L, C Improves speed Can optimize technology for each layer Problems: Dies must be same size Precise alignment is essential Jaap Velthuis (University of Bristol)

Mechanical bonding techniques Direct silicon fusion bonding Mechanical bond only High temperature and pressure Need very flat surface Adhesive bonding Glue Low temperature Jaap Velthuis (University of Bristol)

Electrical+mechanical Copper to copper fusion bonding Press copper surfaces together Need 400oC Copper-tin eutectic bonding Soldering Need 250oC Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) Processing Thinning Wafers can be easily thinned to 50μm, much thinner (6μm) done Making contact Drill hole Fill with Cu Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) 3D sensors (example I) 3 Layer Infrared camera HgCdTe sensor 0.25μm CMOS (analog) 0.18μm CMOS (digital) Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) 3D (example II) 3D Laser rader imager 64x64 array, 30µm pixels 3 tiers 0.18µm SOI 0.35 µm SOI High resistivity substrate diodes Oxide to oxide wafer bonding 1.5µm vias dry etch 6 3D vias/pixel Jaap Velthuis (University of Bristol)

Summary radiation hardness Radiation damage in sensors mainly bulk damage Atoms knocked out of their lattice position extra levels in band gap  Effectively donor removal (type inversion) High leakage currents  High noise Thermal runaway Problems to get full depletion Jaap Velthuis (University of Bristol)

Summary radiation hardness (II) Solutions: n+-on-n or even better n-on-p detectors Material engineering (oxygenated Si/Cz) Cool to cryogenic temperatures (Lazarus effect) Use different materials like diamond Use different detector type like 3D Jaap Velthuis (University of Bristol)

Jaap Velthuis (University of Bristol) Summary Trend towards more integration Sensor and electronics in same device In-device, or in-pixel signal processing Faster, smaller feature sizes Less material Jaap Velthuis (University of Bristol)

Hope you found it interesting Summary Tried to show that Particle Physics is more than hunting for Higgs and CP violation Forefront of Engineering (stiff light weight support structures, cooling, tunnel building) High speed and radiation hard electronics Computing (web, grid, online) Accelerators (e.g. cancer therapy, diffraction) Imaging sensors (e.g. nth generation light source, medical imaging) If you find these things interesting, why don’t you join us? Particle Physics Thanks for attention Hope you found it interesting enough to stay awake Jaap Velthuis (University of Bristol)