Silicon Detectors in High Energy Physics

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1 Thomas Bergauer (HEPHY Vienna) IPM Teheran 22 May 2011

2 Sunday: Schedule Semiconductor Basics (45 ) Silicon Detectors in Detector concepts: Pixels and Strips (45 ) Coffee Break Strip Detector Performance (45 ) Quality Control on strip detectors (45 ) Monday: Radiation Damage (45 ) 22 May 2011 Thomas Bergauer (HEPHY Vienna) 2

3 Detector concepts: Pixels and Strips Single-sided Strip Detectors Two-dimensional Readout Pixel Detectors Other Silicon Detector Structures CCD, Drift Detectors, APD and SiPM, MAPS, DEPFET, SOI, 3D-detectors 22 May 2011 Thomas Bergauer (HEPHY Vienna) 3

4 SINGLE SIDED STRIP DETECTORS 22 May 2011 Thomas Bergauer (HEPHY Vienna) 4

5 The most simple detector is a large surface diode with guard ring(s). no position resolution Good for basic tests (IV, CV) Pad Detector Silicon Detectors in 22 May 2011 Thomas Bergauer (HEPHY Vienna) 5

6 Typical n-type Si strip detector: n-type bulk: ρ > 2 kωcm thickness 300 µm Operating voltage < 200 V. n + layer on backplane to avoid Schottky contact and improve ohmic contact Aluminum metallization Silicon Detectors in DC coupled strip detector Charged particles traversing sensor create e - /h + pairs in the depletion region These charges drift to the electrodes. The drift (current) creates the signal which is amplified by an amplifier connected to each strip. From the signals on the individual strips the position of the through going particle is deduced. 22 May 2011 Thomas Bergauer (HEPHY Vienna) 6

7 Deple%on Voltage (electrical field) p Diode n 22 May 2011 Thomas Bergauer (HEPHY Vienna) 7

8 n-type and p-type detectors Note: The previous slide explains an n-type detector (detector bulk is n-type silicon) Using p-type silicon and exchanging p + and n + would give a perfectly working p-type detector. For tradition and production reasons most detectors used are n-type detectors. p-type detectors have some advantages in high radiation environment (see later). For simplicity I will continue discussing n-type detectors only May 2011 Thomas Bergauer (HEPHY Vienna) 8

AC coupled strip detector AC coupling blocks leakage current from the amplifier. Integration of coupling capacitances in standard planar process.

9 AC coupled strip detector AC coupling blocks leakage current from the amplifier. Integration of coupling capacitances in standard planar process. Deposition of SiO 2 with a thickness of nm between p+ and aluminum strip Increase quality of dielectric by a second layer of Si 3 N 4. AC coupled strip detector: Several methods to connect the bias voltage to the strips 22 May 2011 Thomas Bergauer (HEPHY Vienna) 9

10 AC-coupled sensors create two electrical circuits on the sensor: Readout circuit into amplifier (AC current) Biasing circuit (DC current) Biasing Methods Silicon Detectors in Method to connect readout strips to bias voltage source: Poly-silicon resistor Punch-through FOXFET + h+e- 22 May 2011 Thomas Bergauer (HEPHY Vienna) 10

Biasing Methods: Poly-Silicon Deposition of poly-crystalline silicon between p + implants and a common bias line. Typical sheet resistance of up to R s 4 kω/square.

11 Biasing Methods: Poly-Silicon Deposition of poly-crystalline silicon between p + implants and a common bias line. Typical sheet resistance of up to R s 4 kω/square. Depending on width and length a resistor of up to R 20 MΩ is achieved (R = R s length/width). To achieve high resistor values meandering poly structures are deposited. Drawback: Additional production steps and photo lithographic masks required. Cross section of AC coupled strip detector with integrated poly resistors: 22 May 2011 Thomas Bergauer (HEPHY Vienna) 11

12 Biasing Methods: Poly-Silicon (2) Top view of a strip detector with poly-silicon resistors: 22 May 2011 Thomas Bergauer (HEPHY Vienna) 12

Biasing Methods: Punch through Punch through

) Advantage: No additional production steps

13 Biasing Methods: Punch through Punch through effect: Figures show the increase of the depletion zone with increasing bias voltage (V pt = punch through voltage). 1.) 2.) 3.) Advantage: No additional production steps required. 22 May 2011 Thomas Bergauer (HEPHY Vienna) 13

A gate is implemented on top of a SiO 2 isolation.

14 Biasing Methods: FOXFET Strip p + implant and bias line p + implant are source and drain of a field effect transistor FOXFET (Field OXide Field Effect Transistor). A gate is implemented on top of a SiO 2 isolation. Dynamic resistor between drain and source can be adjusted with gate voltage. 22 May 2011 Thomas Bergauer (HEPHY Vienna) 14

15 Summary: Typical AC-coupled Sensor Most commonly used scheme using poly-si bias resistor 22 May 2011 Thomas Bergauer (HEPHY Vienna) 15

16 TWO-DIMENSIONAL-READOUT 22 May 2011 Thomas Bergauer (HEPHY Vienna) 16

2 nd coordinate requires second detector underneath double the material Acceptable for hadron colliders like LHC Not acceptable for e+/ecolliders with tighter material

17 2 nd coordinate requires second detector underneath double the material Acceptable for hadron colliders like LHC Not acceptable for e+/ecolliders with tighter material budget Stereo Modules Silicon Detectors in Tilt angle defines z-resolutions (usually along beam axis) CMS uses ~6 degrees 22 May 2011 Thomas Bergauer (HEPHY Vienna) 17

Double Sided Silicon Detectors (DSSDs) Advantages: More elegant way for

insulation of n-side (p-stop, p-spray techniques) Very complicated

occupancy Scheme of a double sided strip detector (biasing structures not

18 Double Sided Silicon Detectors (DSSDs) Advantages: More elegant way for measuring 2 coordinates Saves material Disadvantages: Needs special strip insulation of n-side (p-stop, p-spray techniques) Very complicated manufacturing and handling procedures expensive Ghost hits at high occupancy Scheme of a double sided strip detector (biasing structures not shown) real hits Ghosts 22 May 2011 Thomas Thomas Bergauer Bergauer (HEPHY Vienna) 18

Strip Isolation on n-side Problem with n + segmentation: Static, positive oxide charges in the Si-SiO 2 interface. These positive charges attract electrons.

19 Strip Isolation on n-side Problem with n + segmentation: Static, positive oxide charges in the Si-SiO 2 interface. These positive charges attract electrons. The electrons form an accumulation layer underneath the oxide. n+ strips are no longer isolated from each other (resistance kω). Charges generated by through going particle spread over many strips. No position measurement possible. Solution: Interrupt accumulation layer using p + -stops, p + -spray or field plates. Positive oxide charges cause electron accumulation layer. 22 May 2011 Thomas Bergauer (HEPHY Vienna) 19

Picture showing the n + -strips and the p + -stop structure: A.

20 Strip Isolation using p-stop p + -implants (p + -stops, blocking electrodes) between n + -strips interrupt the electron accumulation layer. Inter-strip resistance reach again O(GΩ). Picture showing the n + -strips and the p + -stop structure: A. Peisert, Silicon Microstrip Detectors, DELPHI MVX 2, CERN, 1992 Prototype sensors for Belle II SVD 22 May 2011 Thomas Bergauer (HEPHY Vienna) 20

21 Strip Isolation using p-spray p doping as a layer over the whole surface. disrupts the e - accumulation layer. Often, a combination of p + stops and p spray is being used 22 May 2011 Thomas Bergauer (HEPHY Vienna) 21

Strip Isolation using Field plates Metal of MOS structure at negative

-interface. Above a threshold voltage n + -strips become isolated.

the inter-strip region serve as field plates.

22 Strip Isolation using Field plates Metal of MOS structure at negative potential compared to the n + -strips displace electrons below Si-SiO 2 -interface. Above a threshold voltage n + -strips become isolated. Simple realization of AC coupled sensors: Wide metal lines with overhang in the inter-strip region serve as field plates. A field plate at negative potential interrupts accumulation layer: n + -strips of an AC coupled detector. The alumimnum readout lines act as field plates: A. Peisert, Silicon Microstrip Detectors, DELPHI MVX 2, CERN, May 2011 Thomas Bergauer (HEPHY Vienna) 22

Routing using 2 nd metal layer In the case of double sided strip detectors with orthogonal strips the readout electronics is located on at least two sides (fig. a).

23 Routing using 2 nd metal layer In the case of double sided strip detectors with orthogonal strips the readout electronics is located on at least two sides (fig. a). Many drawbacks for construction and material distribution, especially in collider experiments. Electronics only on one side is a preferred configuration (fig. b). Possible by introducing a second metal layer. Lines in this layer are orthogonal to strips and connect each strips with the electronics (fig. c). The second metal layer can be realized by an external printed circuit board, or better integrated into the detector. (a) (b) (c) 22 May 2011 Thomas Bergauer (HEPHY Vienna) 23

Routing using 2 nd metal layer DSSD with double metal Most complex

SiO 2 or polyimide (common name Kapton) Has been used by DELPHI

with 2 nd metal readout lines (bias structure not shown).

24 Routing using 2 nd metal layer DSSD with double metal Most complex detector 16 layers The isolation between the two metal layers is either SiO 2 or polyimide (common name Kapton) Has been used by DELPHI experiment at LEP 3D scheme of an AC coupled double sided strip detector with 2 nd metal readout lines (bias structure not shown). Alternative Discrete pitch adapter using Kapton flex circuit 22 May 2011 Thomas Bergauer (HEPHY Vienna) 24

Increased coupling and crosstalk between readout and routing lines

25 Double Metal Layer Advantages: routing integrated into sensor Disadvantages: Two more layers on wafer increase complexity Via s Metal Increased coupling and crosstalk between readout and routing lines Thickness of isolation between metal layers is crucial 22 May 2011 Thomas Bergauer (HEPHY Vienna) 25

26 HYBRID PIXEL DETECTORS 22 May 2011 Thomas Bergauer (HEPHY Vienna) 26

27 Hybrid Pixel Detectors Principle pixelated particle sensor amplifier & readout chip CMOS Indium solder bump bonds Clock Inputs Data Outputs Power Connection wire pads power inputs outputs 22 May 2011 Thomas Bergauer (HEPHY Vienna) 27

detector capacitance ( 1 ff/pixel) large signal-to-noise ratio (e.g. 150:1).

28 Pixel Detectors Advantages Double sided strip sensors produce ghost hits - Problematic for high occupancies Pixel detectors produce unambiguous hits 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) 22 May 2011 Thomas Bergauer (HEPHY Vienna) 28

Disadvantages of pixel detectors Large number of readout channels Large number of electrical connections in case of hybrid pixel detectors.

29 Disadvantages of pixel detectors Large number of readout channels Large number of electrical connections in case of hybrid pixel detectors. Large power consumption of electronics Expensive to cover large areas Suitable for innermost region near collision region 22 May 2011 Thomas Bergauer (HEPHY Vienna) 29

Photolithography to precisely define areas for the deposition of the bond material. 3. Deposition, by evaporation, of the bond material (e.g. In or SnPb) producing little bumps ( 10 µm height).

30 Bump bonding process A typical bump bonding process (array bump bonding) is the following: 1. Deposition of an under-bump metal layer, plasma activated, for a better adhesion of the bump material. 2. Photolithography to precisely define areas for the deposition of the bond material. 3. Deposition, by evaporation, of the bond material (e.g. In or SnPb) producing little bumps ( 10 µm height). 4. Edging of photolithography mask leaves surplus of bump metal on pads. 5. Reflow to form balls. L. Rossi, Pixel Detectors Hybridisation, Nucl. Instr. Meth. A 501, 239 (2003) 22 May 2011 Thomas Bergauer (HEPHY Vienna) 30

31 Bump bonding process Electron microscope pictures before and after the reflow production step. In bump, The distance between bumps is 100 μm, the deposited indium is 50 μm wide while the reflowed bump is only 20 μm wide. C. Broennimann, F. Glaus, J. Gobrecht, S. Heising, M. Horisberger, R. Horisberger, H. Kästli,J. Lehmann, T. Rohe, and S. Streuli, Development of an Indium bump bond process for silicon pixel detectors at PSI, Nucl. Inst. Met. Phys, Res. A565(1) (2006) May 2011 Thomas Bergauer (HEPHY Vienna) 31

Hybrid Pixel Module for CMS Sensor: Pixel Size: 150mm x 100mm Resolution σ r-ϕ ~ 15µm Resolution σ z ~ 20µm n+-pixel on n-silicon design Moderated p-spray HV robustness Readout Chip: Thinned to 175µm

32 Hybrid Pixel Module for CMS Sensor: Pixel Size: 150mm x 100mm Resolution σ r-ϕ ~ 15µm Resolution σ z ~ 20µm n+-pixel on n-silicon design Moderated p-spray HV robustness Readout Chip: Thinned to 175µm 250nm CMOS IBM Process 8 Wafer Kapton signal cable 21 traces, 300µ pitch Alu-power cable 6 x 250µ ribbon High Density Print 3 Layers, 48µ thick Silicon Sensor t=285µ 100µ x 150µ pixels µ-bump bonding 16 x Readout Chips (CMOS) 175µ thick SiN base strips 250m thick, screw holes screw holes R. Horisberger 22 May 2011 Thomas Bergauer (HEPHY Vienna) 32

33 OTHER SILICON DETECTOR STRUCTURES 22 May 2011 Thomas Bergauer (HEPHY Vienna) 33

34 Other Silicon Detector Structures Strip and hybrid pixel detectors are mature technologies employed in almost every experiment in high energy physics. Additional interesting silicon detector structures are: Charged Coupled Devices (CCD) Silicon Drift Detectors (SDD) Monolithic Active Pixels (MAPS) Silicon On Oxide (SOI) 3D detectors Depleted Field Effect detectors (DEPFET) Avalanche Photo Diodes (APD) and Silicon Photo Multiplier (SiPM) 22 May 2011 Thomas Bergauer (HEPHY Vienna) 34

Charge Coupled Devices (CCD) Shallow depletion layer

the pixel shifted during readout through the columns final row

35 Charge Coupled Devices (CCD) Shallow depletion layer (typically 15 µm) relatively small signal charge is kept in the pixel shifted during readout through the columns final row to a single signal readout channel: Slow device, hence not suitable for fast detectors. Improvements are under development, e.g. parallel column readout. 22 May 2011 Thomas Bergauer (HEPHY Vienna) 35

Silicon Drift Detectors Bulk fully depleted by p + strips and backplane p + implantation Ionizing particle produces e/h-pairs Holes swept out Electrons move towards collecting anodes (n + ).

36 Silicon Drift Detectors Bulk fully depleted by p + strips and backplane p + implantation Ionizing particle produces e/h-pairs Holes swept out Electrons move towards collecting anodes (n + ). 2-dimensional readout Segmentation of collection anodes Drift time Used for example in the experiment ALICE (CERN) Evolution of Silicon Sensor Technology in Particle Physics, F. Hartmann, Springer Volume 231, May 2011 Thomas Bergauer (HEPHY Vienna) 36

37 Monolithic Active Pixels (MAPS) Scheme of a CMOS monolithic active pixel cell with an NMOS transistor. The N-well collects electrons from both ionization and photo-effect. Evolution of Silicon Sensor Technology in Particle Physics, F. Hartmann, Springer Volume 231, May 2011 Thomas Bergauer (HEPHY Vienna) 37

Silicon on isolator (SOI) A SOI detector consists of a thick fully depleted high resitivity bulk and seperated by a layer of SiO 2 a low resistivity n-type material.

38 Silicon on isolator (SOI) A SOI detector consists of a thick fully depleted high resitivity bulk and seperated by a layer of SiO 2 a low resistivity n-type material. NMOS and PMOs transistors are implemented in the low resitivity material using standard IC methods. Evolution of Silicon Sensor Technology in Particle Physics, F. Hartmann, Springer Volume 231, May 2011 Thomas Bergauer (HEPHY Vienna) 38

Voltage is applied between Depletion is sideways Small distances between the electrodes Very low depletion voltages

39 3D Detectors Silicon Detectors in Non planar detectors Deep holes are etched into the silicon filled with n + and p + material. Voltage is applied between Depletion is sideways Small distances between the electrodes Very low depletion voltages Very fast, since charge carries travel shorter distances Very radiation tolerant detectors, in discussion for inner detector layers at SLHC. Picture from CNM-IMB (CSIC), Barcelona 22 May 2011 Thomas Bergauer (HEPHY Vienna) 39

40 3D Detectors (cont.) Single column: Double-sided double column: Low field region between columns High field, but more complicated 22 May 2011 Thomas Bergauer (HEPHY Vienna) 40

Depleted Field Effect Transistor (DEPFET) Function principle Field effect transistor on top of fully depleted bulk All charge generated in fully depleted bulk assembles underneath the transistor

41 Depleted Field Effect Transistor (DEPFET) Function principle Field effect transistor on top of fully depleted bulk All charge generated in fully depleted bulk assembles underneath the transistor channel steers the transistor current Clearing by positive pulse on clear electrode Combined function of sensor and amplifier Used for Belle II and candidate for ILC 22 May 2011 Thomas Bergauer (HEPHY Vienna) 41

Depleted Field Effect Transistor (DEPFET) Properties low capacitance low noise Signal charge remains undisturbed by readout repeated readout Complete clearing of signal charge no reset noise Full

42 Depleted Field Effect Transistor (DEPFET) Properties low capacitance low noise Signal charge remains undisturbed by readout repeated readout Complete clearing of signal charge no reset noise Full sensitivity over whole bulk large signal for mip. X-ray sensitivity Thin radiation entrance window on backside X-ray sensitivity Charge collection also in turned off mode low power consumption 22 May 2011 Thomas Bergauer (HEPHY Vienna) 42

Avalanche Photo Diode (APD) Operated in reverse bias mode in the breakdown regime Geiger-mode A single photon is able to trigger an avalanche breakdown.

43 Avalanche Photo Diode (APD) Operated in reverse bias mode in the breakdown regime Geiger-mode A single photon is able to trigger an avalanche breakdown. Very temperature sensitive Current increase limited by quenching resistor. D. Renker, Nucl. Instr. Methods A 571 (2007) 1-6 Used for photon detection in calorimeters (e.g the electromagnetic calorimeter of CMS), in Cherenkov counters, etc. 22 May 2011 Thomas Bergauer (HEPHY Vienna) 43

Silicon photo multiplier (SiPM) SiPM are

popular as replacement for standard photo

44 Silicon photo multiplier (SiPM) SiPM are matrices of APDs: Al Front contact R quenching ARC p + silicon wafer Back contact -V bias SiPMs become more and more popular as replacement for standard photo multiplier tubes. 22 May 2011 Thomas Bergauer (HEPHY Vienna) 44

45 Part 2: Detector concepts: Pixels and Strips END 22 May 2011 Thomas Bergauer (HEPHY Vienna) 45

Silicon Detectors in High Energy Physics. Thomas Bergauer (HEPHY Vienna)

Silicon Detectors in High Energy Physics. Thomas Bergauer (HEPHY Vienna) Thomas Bergauer (HEPHY Vienna) VO Teilchendetektoren April 2016 Schedule Today: Semiconductor Basics Detector concepts: Pixels and Strips Strip Detector Performance Radiation Damage Next week: History