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Advanced TCT systems

Advanced TCT systems. G. Kramberger Jo žef Stefan Institute , Ljubljana, Slovenia (most of the work shown was done in the framework of RD48/RD50 collaborations). Outline . Motivation Basic principles of operation Scanning-Transient Current Technique Examples of different applications

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Advanced TCT systems

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  1. Advanced TCT systems G.Kramberger Jožef Stefan Institute, Ljubljana, Slovenia (most of the work shown was done in the framework of RD48/RD50 collaborations)

  2. Outline Motivation Basic principles of operation Scanning-Transient Current Technique Examples of different applications Beyond high energy physics Conclusions G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  3. Motivation • Transient current technique (observing effects of non-equilibrium carriers in different devices) dates in the 1960s. • From 1990s on the technique was widely used in studies of semiconductor detectors – materials, mostly pad detectors after irradiation • space charge • effective trapping times • charge collection efficiency • In recent decade the use of Scanning-TCT (focused laser beam) combined with new ways of using it has become a very useful tool to study segmented devices. The aim of this work is to: • Explain some basics of TCT • Give some practical advices on construction of a TCT system • Review different ways of using TCT G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  4. 3.) DAQ Basic principles of operation 1.) laser + optical system digital oscilloscope HV sample 2.) Biasing & amplifier TCT measurement - monitor the current induced by motion of carriers rather than only charge(normal way of detector operation in particle physics). The price is the sensitivity – much more generated charge is needed for detection – mip particles can not be measured. Usually light is used to generate e-h pairs, but can be also a, m beam. G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  5. Basic principles of operation (lasers) • But also disadvantage over the a, m-beam: • use for wide band gap semiconductors difficult Eg<hn (hard to get fast pulsed lasers) • effects of field screening – plasma/ recombination, particularly of importance when focused to few mm • the structure needs to have opening in the metallization – can not study all the volume • laser pulse is not infinitely short 50 ps with tails of few 100 ps • Creation of charge by laser has many advantages over the particles: • averaging (no problem with noise) • triggering (exactly known time of laser pulse) • generation depth can be tuned by wavelength • intensity tuning – but hard to have absolute scale • controllable beam position • Laser pulse should be as short as possible (vsat=100mm/ns, pulse<<1ns), but, • pay attention to long tails (can depend on power and wavelength) – high power is needed for certain applications • jitter (pulse-trigger) is very important and can effectively spoil the resolution • no need to go extremely “short” if other parts of your system are not fast enough • Variable pulse width and fast repetition rate can be useful in several studies (rate effects, trapping/detrapping) • Stability G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  6. Basic principles of operation (lasers) 100 nm at 405 nm • Light absorption in Si: • mip like 1064 nm • m beam like 980 nm • near surface 660 nm • surface 405 3 mm at 640 nm 100 mm at 980 nm 1 mm at1064 nm In other materials: SiC – ~3-3.2 eV (405 nm) C – 5.5 eV (223 nm) • Absolute calibration and laser intensity • Apart from relative comparison of waveforms at different position/bias/T, absolute measurements can/could be performed with calibrated device) • Better to adjust it with neutral density filter than electronically if pulses are distorted neutral density filter Calibrated device Beam splitter Device under test G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  7. Basic principles of operation (electronics) • Two configurations: • With Bias-T (simple housing&grounding), but Bias-T can influence the measured waveforms • Without Bias-T (complicated housing&grounding&cooling), but easier multichannel operation HV HV • Bias-T : pay attention to: • Frequency response (the bandwidth of the circuit is important, depending on your application ) • HV capability (not many available for >1000 V) • Wide band current amplifier : • Frequency response • Gain – depends very much on application/laser color (10 dB – 53 dB) – should be as high as possible to be sensitive for low signals, but signals should match the dynamic range of your ADC • Connections: • make sure everything is shielded with as few of “patch-connections” as possible. • Impendence matching (ideally frequency independent impendence) G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  8. Basic principles of operation (signal) I trapping detector geometry holes ( e0∙Ne-h) Generation/ Recombination electric field electrons (- e0∙Ne-h) +HV Example - LGAD(Virginia’s talk) 3.) 1.) drift of electrons 4.) 2.) onset of multiplication 5.) 3.) end of multiplication 2.) 6.) 4.) drift of holes 1.) 5.) end holes drift 6.) tail (diffusion + electronics) G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  9. Basic principles of operation (analysis) induced current laser pulse measured transfer function In general a complicated task to extract I(t) from the measured current. For most of the systems roughly the following two assumptions can be made: R=input impedance of the amp. C=connected electrode capacitance which allow for solution in time domain (no need for FT) If, however, you are looking in effects on timescale longer that few 100 ps: Im(t)~I(t) Transfer function of electronics is crucial and depends on many things – mostly on amplifier, bias-T, oscilloscope (can be measured with very thin sample 25 mm where the current pulse is very short) G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  10. Basic principles (pad diodes) Portable TCT system (exhibited at the workshop) • Space charge/electric field (double junction/space charge inversion) from I(t): V. Eremin et al, Nucl. Instr. and Meth. A 372 (1996) 388. + very long list • Charge collection efficiency/multiplication J. Langeet al., Nuclear Instruments and Methods in Physics Research A 622 (2010) 49–58. J. Langeet al.,. PoS(Vertex 2010) 025. + very long list • Effective trapping times: • “Charge Correction Method” – based on Q(V>Vfd)~const. in absence of trapping – correct current pulse for trapping to achieve this. T.J. Brodbeck et al., Nucl. Instr. and Meth. A455 (2000) 645. G. Kramberger et al., Nucl. Instr. and Meth. A 481 (2002) 297-305. O. Krasel et al., IEEE Trans. NS 51(1) (2004) 3055. A. Bates and M. Moll, Nucl. Instr. and Meth. A 555 (2005) 113-124. +long list • Detrapping times G. Kramberger et al JINST 7 (2012) P04006 G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  11. Scanning TCT system A position resolved TCT Two modes of operation: Top-TCT and Edge-TCT: Top-TCT Edge-TCT G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  12. Scanning Transient current system see: www.particulars.si for additional info G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  13. Optical system Galilean beam expander iris focusing lens fibre coupled laser NDF ~20 mrad opening angle FWHM~10 mm IR Refractive index helps to achieve narrower beam width in Si than measured at the surface Si Most of the system use fiber coupled lasers (no need to correct for astigmatism) The thinner the core the better focus can be achieved (4 mm is standard) Focus is usually measured by “knife edge technique” where the light crosses the edge of metallization G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  14. Connections in multi-electrode systems HV HV HV Implants connected to bias resistor Implants connected to bias resistor HV Always bond neighboring strips – otherwise they act as interpolation strips! Irradiated sample Neighbors bonded to low impedance Neighbors not bonded Remember Ew plays a role in operation of silicon detectors G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  15. Multi-channel operations (3D-STC example) metal 3D-stc DC coupled detector (1st FBK 3D) (64 x 10 columns) 80 mm pitch 80 mm between holes 10 mm hole diameter 150 mm n+ p+ 300 mm p n+ p+ 3 channels connected in parallel G. Kramberger et al., 6th RD50 Workshop, Prague, 2006 Red laser illumination G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  16. Examples of applications (strip profiling) Feq=1015 cm-2 Feq=5∙∙1015 cm-2 Connected to amp. Observation of “Trapping induced charge sharing“ – non complete drift results in charge induced in other strips – for p-type detectors it is of the opposite polarity (G. Kramberger et al., IEEE Trans. NS 49(4) (2002) 1717) The induced charge in the inter-strip region becomes larger than close to the strips – field focusing and more multiplication (I. Mandić et al., 2013 JINST 8 P04016) G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  17. Examples of applications (strip profiling) direction of the scan Guardring 5x5 mm spaghetti diodes Ew similar to diode E equal to strip sensor All strips ganged together. Feq=2∙1015 cm-2 5120 min@60oC no metal charge collection profiles: metal • enhanced multiplication at the edge of implants • Non-uniform charge collection along the strips G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  18. Edge-TCT G. Kramberger et al.,IEEE Trans. Nucl. Sci. NS-57 (2010) 2294. 10kHz-2.5GHz 1.5 GHz scope laser • 1060 nm • ~100 ps pulse • ~200 Hz repetition lens system Constant The trapping can be completely taken out of the equation! (The major obstacle of extraction of physics parameters from time evolution in conventional/Top-TCT is severe trapping) G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  19. Charge collection and velocity profiles CHARGE COLLECTION PROFILE Vfd~16 V VELOCITY PROFILE ve+vh [arb.] charge collection for mip G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  20. Examples of applications (E-TCT on strips) Feq=5∙1015 cm-2 1000 V neutron irradiated G. Kramberger et al.,IEEE Trans. Nucl. Sci. NS-57 (2010) 2294. Velocity profile in heavily irradiated silicon detector – field modeling in irradiated silicon detectors • Active SC region • Neutral bulk • Back SC region Micron SSD Pitch 80 mm Implant width 20 mm Thickness 300 mm First direct observation of charge multiplication in induced current for irradiated silicon strip detectors G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  21. Examples of applications (3D detectors) 3Dstrip detectors processed by CNM 230 mm thick Strip pitch 80 mm Column width 10 mm overlap= 150 mm T=-20oC Feq=5∙1015 cm-2 Profiling of CCE within the cell Multiplication seen in induced current NON-IRRADIATED-20 V Charge multiplication G. Stewart et al., JINST Vol. 7 (2013) . G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  22. Examples of applications (HVCMOS) G. Kramberger et al., 24th RD50 Workshop, Bucharest, 2014 FWHM~7 mm beam Probing of collection properties in very highly doped substrates (1015 cm-3) Good separation of diffusion and drift components (not possible with CCE charge collection efficiency measurements) See preliminary results for irradiated detectors in Daniel’s talk G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  23. Examples of applications (SCP detectors) Vbias[V] M. Christophersen et al., NIM A 699 (2013) 14. Vfd~50 V 660 nm current pulses after illumination with RED laser Velocity profile at detector edge – profiling of the edge fields Vfd~50 V I. Mandić et al., NIM A 751 (2014) 41. Scribe-Cleave-Passivate is a technique for making slim edge detectors: basically passivate edge of cleaved detector by Al2O3 which is negatively charged – high resistance of the edges G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  24. preliminary Beyond HEP (solar cells) Laser beam charge collection profile impact of recombination • “Dirty poly-crystalline silicon”, very low resistivity <few Wcm • Solar cells • minority carrier lifetime/ recombination/diffusion studies • studies of hetero-structure properties • Quality assurance of the material G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  25. Beyond HEP (de-trapping in semicoductors) G. Kramberger et al JINST 7 (2012) P04006 1. 3. DQ 2. Vfd~40V Vfd • Charge in irradiated sensor is trapped on the timescale of tens ns • The amount of the charge trapped charge decreases for larger Vbias • Trapped charge is released and measured on much larger time scale Another flavor of this technique is I-DLTS by using TCT (C. Gallrapp, presented at 24th RD50, Bucharest, 2014) Flooding the detector with free carriers at different T and looking for the charge released (same as 3.) G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  26. preliminary Beyond HEP (RadFET studies) Exploit different wavelength to separate bulk from interface effects l=660 nm l=405 nm -VG P+ -Vs P+ GND N • Additional carriers generated near the surface drift over the entire channel and give rise to transient current pulse! • Idea behind this technique is to measure the transient current analyze it and extract parameters related to surface damage such as: • oxide charge • trapping at the interface • density of interface states (recombination velocity) G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

  27. Conclusions TCT has been around in HEP for almost 20 years, first as a tool used to study material properties on pad detectors. A workhorse of RD48/50 collaborations. Scanning-TCT systems are excellent tools to study properties of segmented detectors. Powerful analysis techniques have evolved along. It has potential use also outside HEP and for educational purposes Systems have become commercially available G. Kramberger, Advanced TCT systems, Vertex 2014, Lake Macha, 15-19.9.2014

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