Silicon strip detectors and their readout electronics Francis

Silicon strip detectors and their readout electronics Francis Anghinolfi CERN December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 1

OUTLINE • Silicon strips detectors for tracking • (Micro)Electronics for silicon strips • Strips readout examples NB : I will not talk about silicon pixel detectors nor silicon drift detectors …. . December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 2

Silicon Strips Detectors PROS • Solid State • ~100% efficient for particle detection • Small (best when …. ) CONS • No multiplication Small signals, then need smart electronics to detect the signal (large amplification and noise reduction) • Leakage (DC) current December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 3

Silicon Strips Detectors Solid state • No gas, no liquid stable material • But as a consequence, subject to radiation degradation • Benefits from silicon wafer industry environment (access to very pure silicon material, precise alignment machines, clean room technologies etc …) December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 4

Silicon Strips Detectors Efficiency SIGNAL if there is PARTICLE Detection Efficiency close to 100% Charge is always generated by a MIP crossing particle December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 5

Silicon Strips Detectors Efficiency SIGNAL if there is PARTICLE Detection Efficiency close to 100% Inefficiency may result from : ØInsensitive areas (edges) ØCharge sharing ØTraps or defect December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 6

Silicon Strips Detectors ++++ -----c Signal formation in Silicium • High Energy Particle deliver signal in the depletion region, by electron hole pair creation. Positive and negative charges drift in presence of the applied electric field December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 7

Silicon Strips Detectors Signal formation in Silicium • The depletion region is obtained by applying a voltage between top and bottom of the detector • For large voltage and small doping concentration it is possible to obtain the depletion of the full volume December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 8

Silicon Strips Detectors Signal formation in Silicium The diode (p-type over n-type bulk in this figure) is needed to block direct current path. Direct current path could be as high as m. A per strips ( a killer for signal detection) The diode is reverse biased. The dynamic signal from particle track is sensed through the capacitance of the blocking diode December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 9

Silicon Strips Detectors Signal formation in Silicium • The signal is formed by electron-hole pair creation along the track path The energy loss for a Minimum Ionizing Particle (MIP) is around 260 e. V/um for 300 um thick silicon. One e-h pair creation energy in silicon is 3. 62 e. V • for a fully depleted silicon volume 300 um thick the average signal is around 22000 electrons (3. 5 f. C) December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 10

Silicon Strips Detectors Charge sharing Strip pitch Strip length In case of track angle the charge distributes on adjacent strips e- e- ee- Particle track through Si material December 1, 2009 Collected Charge quantity depends on the depleted silicon thickness The charges are drifting along the electrical field toward the strips. The electronics channels are connected to the strips (directly or through decoupling capacitors) F. Anghinolfi CERN/PH/ESE Seminar 11

Silicon Strips Detectors Signal formation in Silicium • The collection time is usually below 10 ns for electrons (drifting to one side) and below 25 ns for holes (drifting the other side) • Good time resolution is also possible (~ few ns range, OK for LHC with 25 ns bunch interval) December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 12

Silicon Strips Detectors The Signal is small For example read the signal on 50 ohms resistor : Typical 3. 5 f. C delivered on 50 ohms in ~10 ns results in peak voltage of 17 u. V The voltage noise of the 50 ohms resistor in the bandwidth required for signal is ~ 3. 5 u. V rms The ratio (5), is not enough to provide safe signal detection (additional noise sources, charge sharing etc …) December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 13

Silicon Strips Detectors The sensing geometry (strip size) can be small • Small is good for tracking detectors : 1020 um position resolution attainable (less for pixels) • Small geometry is beneficial for the signal detection electronics …. December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 14

Silicon Strips Detectors Small is good for the detection • Small areas are obtained by the detector segmentation • There is no signal loss (dead areas) even with segmented detectors • Small areas have less leakage current and less capacitance, 2 key items which improve the signal detection (signal over noise ratio SNR) December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 15

Silicon Strips Detectors Example : Segmented detector This detector is made of 4 rows of 1280 strips of length 2, 5 cm. The strip pitch (horizontal axis) is 80 um. The expected resolution is 23 um in X. (Development for ATLAS upgrade, KEK, Japan) 4 rows of 2. 5 cm long strips 2, 5 cm 1280 strips on ~ 10 cm December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 16

Silicon Strips Detectors What we know about electronics for Silicon Strips • Has to deal with small signal and leakage current • Small detector segments have less leakage current and less capacitance, 2 key items which improve the signal detection (signal over noise ratio SNR) • But more channels to cover a fixed detecting area : It creates a trade-off between power (nbe of channels) versus SNR December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 17

Readout Electronics Typical “front-end” elements The electronics circuit is necessary for : + Rp - signal amplification (signal multiplication factor) Z noise rejection signal “shaping” Particle Detector Electronic Circuit Impedance adaptation Final objective : Signal detection Amplitude measurement Time measurement December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 18

Readout Electronics • Impedance adaptation • Amplitude resolution • Time resolution • Noise cut High Z Low Z + Rp - Circuit Voltage source Zo Z Low Z T Low Z output voltage source circuit can drive any load Output signal shape adapted to subsequent stage (T/H, ADC, Discriminator) Signal shaping is used to reduce noise vs. signal December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 19

Readout Electronics x(f) Noise floor (white) f 0 y(f) h(f) y(f) f f 0 f f Improved Signal/Noise Ratio Example of signal filtering : the above figure shows a « standard » filter case, where only noise is filtered out. December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 20

Readout Electronics x(f) y(f) h(f) x(f) Noise floor y(f) f f 0 f f Improved Signal/Noise Ratio In particle physics, the input signal, from detector, is often a very fast pulse, similar to a “Dirac” pulse. Therefore, its frequency representation is over a large frequency range. The filter (shaper) provides a limitation in the signal bandwidth and therefore signal shape at the filter output is different from the input signal shape. The output signal shape, different from the input detector signal shape, is chosen to optimize the Signal-to-Noise Ratio • Doing this there is a trade-off btw. SNR, power and pile-up December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 21

Readout Electronics Filter cuts noise. Signal BW is preserved f 0 f Filter cuts inside signal BW : modified shape f 0 December 1, 2009 f F. Anghinolfi CERN/PH/ESE Seminar 22

Readout Electronics I d(t) Preamplifier Shaper O Q/C. n(t) What are the functions of preamplifier and shaper (in ideal world) : • Preamplifier : is an ideal integrator : it detects an input charge burst Q d(t). The output is a voltage step Q/C. n(t). Has large signal gain such that noise of subsequent stage (shaper) is negligeable. • Shaper : a filter with : characteristics fixed to give a predefined output signal shape, and rejection of noise frequency components which are outside of the signal frequency range. December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 23

Readout Electronics I Preamplifier Shaper t t Q/C. n(t) f d(t) = 1/s f CR_RC 4 shaper Ideal Integrator T. F. from I to O O x RCs /(1+RCs)5 = RC/(1+RCs)5 Output signal of preamplifier + shaper with “ideal” charge at the input t December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 24

Readout Electronics I d(t) Shaper Preamplifier Non-Ideal Integrator 1/(1+T 1 s) O CR_RC shaper Integrator baseline restoration x RCs /(1+RCs)2 Non ideal shape, long tail December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 25

Readout Electronics I d(t) Preamplifier Non-Ideal Integrator T. F. from I to O 1/(1+T 1 s) Shaper Integrator baseline restoration x O CR_RC shaper (1+T 1 s) /(1+RCs)2 Pole-Zero Cancellation Ideal shape, no tail December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 26

Readout Electronics Pile-up • The detector pulse is transformed by the front-end circuit to obtain a signal with a finite return to zero time CR-RC : Return to baseline > 7*Tp 1 2 3 4 5 8 7 CR-RC 4 : Return to baseline < 3*Tp 1 December 1, 2009 2 F. Anghinolfi CERN/PH/ESE Seminar 3 27

Readout Electronics For the requirement of strips readout for the LHC experiments, the shaping (peaking) time should be in the order of 25 ns It allows discrimination of events as close as 75 ns With the CR-RCn circuits as described above, it is difficult to trade 25 ns peaking time with low power circuit December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 28

Readout Electronics Different solutions have been implemented to realize low power and fast (25 ns) shaping time for the LHC experiments: • transimpedance amplifiers • analog signal processing December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 29

Readout Electronics Transimpedance Amplifier For ideal Amplifier A Resistive feedback element The main pole is function of the detector input capacitance Rf Other poles are coming from the amplifier open-loop transfer function. iin(t) A Cd Vout Amplifier Detector model The preamplifier does a fraction of the shaping function But this circuit is critically stable and needs careful design The feedback element Rf contributes to the noise December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 30

Readout Electronics Analogue Signal Processing Analogue sampling and storage Analog Processor, 25 ns shaping time 1 of the 128 channels Charge preamp programmable gain 50 ns shaper unity gain inverter charge SF preamplifier differential 128: 1 current MUX output stage analogue pipeline shaper SF S/H APSP The fast shaping is applied only to selected samples of the signal, therefore there is a gain in power December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 31

Readout Electronics The Signal-to-Noise Ratio Whatever is the solution choosen to realize the shaping function, the overall Signal -to-Noise depends on the overall electronics circuit transfer function up to the measurement output The signal is from the detector, the noises are from the active (transistor, diode) and passive (resistors) elements Resistance in serie Rs 4 k. TRs G(f) Cd 2 q. Ishot Rp 4 k. TRp December 1, 2009 Input transistor (under assumption that load does not contribute, and that the input gain stage is high enough to neglect 2 nd stages contribution…) Resistance in parallel Diode (for strips : reverse bias F. Anghinolfi CERN/PH/ESE Seminar diode) 32

Readout Electronics The Signal-to-Noise Ratio In case of strips : Strip capacitance Not present Rs 4 k. TRs Input device “channel” noise G(f) Cd 2 q. Ishot Rp 4 k. TRp Bias resistors Reverse bias diode leakage December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar Front-end circuit with shaping time constant t 33

Readout Electronics The Signal-to-Noise Ratio • All noise contributions are calculated in terms of noise voltage appearing at the input of the amplifier • Noise sources are from detector element and from amplifier. 4 noise sources are considered here : 1. 2. 3. 4. December 1, 2009 Ishot current in diode (leakage current in Si Detector element ) Rp noise, (any) resistance in parallel to the input Rs noise, (any) resistance in serie with the input V 2 na equivalent input noise of the input device of the amplifier F. Anghinolfi CERN/PH/ESE Seminar 34

Readout Electronics The Signal-to-Noise Ratio t is the shaping time (0 to Rs 4 k. TRs G(f) Cd 2 q. Ishot Rp 4 k. TRp A formulation of the noise in “electrons” is given here for the CR-RC 2 transfer function G(f) The signal-to noise ratio is computed by division of the signal expressed in electrons by the ENC calculated with the formula December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar peak) of the CR_RC 2 shaping function V 2 na is the equivalent voltage noise source of the amplifier input device gm is proportional to the square root of the current in the input device 35

Readout Electronics The Signal-to-Noise Ratio Formulation without diode current, without Rs Increase transistor current (power !) To reduce ENC Small detector segment Shaping time tradeoff CR-RCn “n” factor dependance December 1, 2009 n 1 2 3 4 5 6 7 Fs 0. 92 0. 84 0. 95 0. 99 1. 11 1. 16 1. 27 n 1 2 3 4 5 6 7 Fp 0. 92 0. 63 0. 51 0. 45 0. 40 0. 36 0. 34 F. Anghinolfi CERN/PH/ESE Seminar 36

Readout Electronics The Signal-to-Noise Ratio ENC (el. ) C=15 p. F optimum C=10 p. F C=5 p. F Shaping time (ns) ENC dependence to the shaping time (C=10 p. F, gm=10 m. S, R=100 Kohms) December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 37

Readout Electronics The Power vs. other parameters trade-off This (approximate, don’t use it in real life !) equation shows the relationship btw. the front-end power (input branch only !), detector capacitance and noise performance Numerical example : Target 10 p. F detector, ENC as 500 el. t=25 ns, V= 2. 5 V P = 0. 32 m. W (strips typical) Target 0. 2 p. F detector, ENC as 120 el. t=25 ns, V= 2. 5 V P = 3 m. W (pixel case) December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 38

128 x 192 bias gen. CAL pipe logic 8. 1 mm December 1, 2009 APSP + 128: 1 MUX pipeline FIFO 7. 1 mm 128 x preamp/shaper Readout System for highly segmented Si Strips detectors APV 25 description control logic The CMS silicon tracker analogue architecture; 128 channels of preamplifier/shaper followed by one analogue memory (pipeline) bank. The APSP is the final “fast” shaping circuit, acting on selected signal samples The readout is analogue : reading amplitude allows to measure charge sharing across adjacent strips F. Anghinolfi CERN/PH/ESE Seminar 39

Readout System for highly segmented Si Strips detectors ABCD/N description The ATLAS silicon tracker binary architecture; 128 channels of preamplifier/shaper/compar ator with two memory banks, one for trigger latency and one readout buffer The readout is binary (either above or below a programmable threshold). Low threshold setting is required to not loose signal in case of charge sharing December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 40

Readout System for highly segmented Si Strips detectors Beetle FE chip The LHCb VELO frontend chip tracker has 128 channels of preamplifier/shaper/discrimi nator followed by one analogue memory (pipeline) bank. Either analogue or binary data is stored into the pipeline. The readout is analogue but both amplitude or binary information can be readout. December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 41

Readout System for highly segmented Si Strips detectors Performance and system aspects for the LHC experiments Parameter Number Spatial precision 20 um range Channel count ~10 M (CMS, ATLAS) Channel power 3 -5 m. W SNR Above 10 after radiation damage Linearity a few MIPs Long term performance Should work for 10 “LHC years” Radiation tolerance LHC radiation levels ~10 Mrad and 2 10^14 eqvlt 1 Me. V neutrons December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 42

Readout System for highly segmented Si Strips detectors PHOTOS The VELO tracker detector of LHCb: The electronics (Beetle) are on the PCB circling around the radial strips December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 43

Readout System for highly segmented Si Strips detectors PHOTOS The CMS tracker module : Two large planes detectors are connected together by bonding to get long strips (20 cm). The electronics (APV 25) are on the small PCB at the end of the silicon detector December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 44

Readout System for highly segmented Si Strips detectors PHOTOS View of one fraction of the CMS tracker, showing detecting planes and the associated electronics and cabling December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 45

Readout System for highly segmented Si Strips detectors PHOTOS December 1, 2009 View of one disk of the CMS tracker end-cap: detectors with strips form a “V” shape F. Anghinolfi CERN/PH/ESE Seminar 46

Readout System for highly segmented Si Strips detectors View of one barrel of the ATLAS SCT tracker. December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 47

Readout System for highly segmented Si Strips detectors PHOTOS Details of the electronics FE parts on the ATLAS barrel modules December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 48

Silicon strips are candidate for the LHC experiments upgrade • • Outer Layers – long strips – 2 Layers R= 81. 4, 95. 4 cm – Granularity 12 cm x 80 um – Z length 2 x 190 cm Middle Layers – short strips – 3 layers at R=38, 47. 3, 57. 4 cm – Granularity 3 cm x 80 um – Z length 2 x 100 cm SLHC ATLAS expected Tracker Occupancy (P. Nevski) December 1, 2009 Barrel Disks Section of projected SI Tracker geometry (Nov. 08) Example of Barrel layout R. Nickerson, Oxford F. Anghinolfi CERN/PH/ESE Seminar 49

ABCN-25 : Silicon Strip Module/Stave Readout Concept (ATLAS) ~ 1. 2 meter 61440 strips on each side Cross section Sensor, Hybrid, ASIC Module #1 Cooling In Cooling Pipe Module #2 Module #12 Opto 10 cm TTC, Data & DCS fibers Carbon Honeycomb SC DCS env. IN DCS interlock Cooling Out PS cable SMC Hybrid MC MC MC Service bus ~1. 2 m December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 50

Thank you ! December 1, 2009 F. Anghinolfi CERN/PH/ESE Seminar 51