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Si-Detector Developments at BARC

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1 Si-Detector Developments at BARC
Dr. S.K.Kataria Electronics Division, BARC, Mumbai

2 Collaborators M.D. Ghodgaonkar, Anita Topkar, M.Y. Dixit, V.B. Chandratre, A.Das, Vijay Mishra, V.D. Srivastava, R.V. Shrikantaiah, Acharyulu, R.K. Choudhari, Bency John,A.K. Mohanty BARC H.V. Ananda, Subash Chandran, Prabhakararao, N. Shankaranarayana BEL O.P. Wadhawan, G.S. Virdi CEERI R.K. Shivpuri, Ashutosh Bharadwaj, Kirti Ranjan: DU BARC has been developing and producing Surface Barrier Silicon detectors of several types for physics experiments for decades. These have been used for charged particles, x-rays and beta particle detection in the Vandegraff and Pelletron accellerators experiments. In 1997, we started work on the development of the PIPS Silicon detectors using IC fabrication labs in the country. PIPS Detectors are passivated ion implanted Silicon detectors which have can be developed at the standard IC-fabrication facility. As these developments are carried at the commercial foundries, the process details were not available. Therefore, we started with a large development team of scientists who have been working in the area of surface barrier detector development at BARC, IC fabrication teams at CEERI and BEL, Detector Simulation groups at BARC and Delhi University with the aim to develop the Silicon detector technology in the country. This development work has now been completed with the contributions from all the institutions.

3 Plan of the Talk Development of the CMS preshower silicon strip detector Silicon Drift Detectors Si-Detector Readout Electronics I shall also like to mention the contribution of micro-electronics group of IIT Mumbai who have always given us advice whenever we faced any difficulty in the development of the process.I would also like to thank the HEP community for their faith in our team that we shall be able develop the very large area Silicon strip detectors which can be used in the CMS experiment and therefore gave full financial support to the development of PIPS technology in the country. I can further say that we not only have developed Silicon strip and pixel detectors but also can design more complex Silicon Drift detectors with built in DEPJFET. Such studies are being carried out by Ph D students at BARC now. With the low noise amplification only, the benefits of the good PIPS detectors can be useful. We have developed some very low noise CMOS analog ASIC’s for use as front end applications. I shall also mention these in the last part of talk.

4 Compact Muon Solenoid CMS
Coming to our participation in the CMS experiment, India CMS collaboration will be developing ¼ of the Silicon strip detectors in the Preshower Detector Subsytem and also the design of the readout electronics from these detectros.

5 Preshower Disc Total 124 x 4 = 496 Mother boards ~2.49m MB TYPE2
K Chip Total 124 x 4 = 496 Mother boards The preshower detector consists of 4 discs of Si strips, 2 on each end-cap side. The picture shows one of such discs. Each rectangle represents motherboard which supports the Si strip detectors (micromodule) and accommodates the front-end electronics.

6 Advantages of silicon detectors:
Fast response of the order of few ns High level of segmentation possible- strips, microstrips, pixels,etc High energy and position resolution Room temp operation possible Use of silicon IC technology enables batch fabrication with very good uniformity & low cost of production Silicon strip detector is the ideal choice for Preshower application where the position accuracy required is less than 100 micron with a pitch of 2 mm.

7 Applications of Silicon Detectors: Detection of radiation - , , , protons, neutrons, charged particles, photons Silicon detectors with multielement geometries of strips, microstrips, pixels, etc - Physics experiments such as that at CERN, Nuclear Science experiments in our country - Astronomy ( low energy X-rays) - Medical imaging (pixel detectors) Single element detectors Small area diodes – area mm2 Personal dosimeters / area monitors for γ-radiation Neutron dose measurement using boron coating/thin foil Low energy X-ray spectroscopy with preamp ( low noise) at –100C ( <60KeV with few 100 eV resolution) High resolution -spectroscopy Charged particle detection Large area diodes mm2 Detection of low activity radiation such as 239 Pu in air Silicon photodiode/scintillator system skip

8 Various types of silicon strip detectors used for high energy physics experiments & other applications Single sided and double sided Strip detectors ( DC coupled, 2D Position sensing) Pixel detectors (suitable for imaging applications) Silicon microstrip detectors ( AC coupled, single or double sided) Silicon drift detectors ( high energy and position resolution, suitable for imaging applications) Monolithic active pixel detectors Single element detectors with high energy resolution/large sensitive area pass

9 Silicon strip/microstrip detector ( SS, DC coupled)
Schematic of silicon strip.

10 Active Pixel Detectors Monolithic – Has readout inside the detector substrate Hybrid – Readout is bump bonded to the pixel pass

11 CMS Preshower Silicon Strip Detector Development (These detectors will be used as the preshower detectors for photons in the CMS at CERN). Prototype Development phase (CEERI and BEL) Preproduction (BEL) Production (BEL) Important activities involved: Detector design and fabrication Detector qualification Micro module assembly During , the R&D of the fabrication process was carried out at CEERI, IV test equipment was developed at BARC. 16 channel strip detector was demonstrated on 2-inch wafer in 1999. During , BEL started the process R&D ED made CV system as well. Eight process runs were made which lead to the final process selection for meeting the requirements of PSD

12 Prototype / Technology Development
16-strip silicon detector developed at CEERI on a 2” Wafer strips of geometry 20x1.65 mm2 enclosed in three P+ guard-rings 32-strip silicon detector of geometry 60x60 mm2 developed at BEL strips of geometry 60x1.69 mm2 enclosed in seven P+ guard-rings PIN diode detectors of various areas – 3x3 mm2 – 10x10 mm2 developed at BEL along with strip detector 70 diodes enclosed in two guard rings Silent features of the silicon strip detectors with three and seven guard rings

13 Detector specifications and Detector design
Electrical Breakdown voltage for all strips >= 300V/500V Total current of all strips =< 5 μA at full depletion voltage (VFD) and <= 10 μA at 150+VFD Maximum 1 strip with leakage current > 1 μA at VFD & > 5 μA at VFD+150V Geometrical Length mm Width , -0.1 mm Detector specifications are very stringent as these are to be operated in a high radiation background of neutrons ( 2x10 14 /cm2) & gamma ( 10Mrad) for a long period of ten years

14 Scanned picture of BEL and CEERI Detectors ( Prototype)
First MASK at BEL for 4-inch wafer and at CEERI for 2-inch wafer

15 Characterization of the strip detector
Probe-jigs to make contact to the 32 strips simultaneously Simulaneous measurement of strip current of 32 strips ( IV) Simulaneous measurement of strip capacitance of 32 strips ( CV) Probe-jigs, measurement setups were developed by BARC. Testing facility has been setup at BEL for qualification of detectors as per the CERN specifications IC Fabs have test equipment only upto 100 volts maximum and for handling small devices 5x5 mm. We had to develop the mounts for the large area detectors, IV and CV systems for 1000 volts operation and my colleagues in ED developed the complete system for IV and CV measurements which were compared with the Keithly Instruments available at CERN and DU afterwords.

16 Argon implantation at Back plane Sacrificial Oxide Grown
During the eight runs in two years we found that sacrifacial oxide growth as the first step argon implantaion at the back plane are essential cleaning processes for very low leakage and HV devices Argon implantation at Back plane Sacrificial Oxide Grown

17 Back-Plane Ohmic Side Processing Technology
Single step implantation Energy of the ion-beam: 80 KeV Dose: 7E15 ions/cm2 Annealing: 30 min, 950 ºC in N2 Double step implantation First Step: Energy of the ion-beam: 110 KeV Dose: 1E15 ions/cm2 Annealing: 10 min, 1050 ºC in O2 + N2 Second Step: Energy of the ion-beam: 50 KeV Dose: 1E16 ions/cm2 For very HV operation when the detector is biased 2-3 times the full depletion voltage, double step implementaion is very useful.

18 Results of IV with and wthout double implantation

19 IV and CV measurement system developed by BARC

20 Reverse IV characterstics of all 32 strips of a detector ( production phase)

21 Capacitance vs Voltage Characterstics of all 32 strips of a detector ( Production phase)

22 Measurement carried out till 500V, BV is > 500V
Full depletion depth voltage changes by +-10% only.

23 Total leakage current at VFD is .1 Microamps
and at 300 V is aboout 1 microamps over the large area of 40 cm2

24 Scribing process is also well established, not much wastage during the scribing process and testing as well.

25 Micromodule assembly The detector is mounted on the ceramic which would have the radiation hard front end hybrid The ceramic is mounted on an aluminum tile Alignment accuracy of about 100 microns is required Mechanical jigs would be used for alignmnet during assembly Ready for the module making but yet to receive the final procedure details from CERN

26 Detector Micromodule

27 Fabrication of Detectors of modified geometry (63 × 63 mm2)
The first batch of detectors using Mask2 and Mask3 has been fabricated at BEL. The processing steps for fabrication of the detectors are the same as the one concluded after batch-7 and repeatability affirmed after batch 8 We have designed two masks for the production batches one with seven guard rings and another with four guard rings. We are using four guard rings one as it gives better yield upto percent IV characteristics of 32 strips a 63 × 63 mm2 detector fabricated at BEL Composite diagram for all the layers of Mask2

28 Doping Profile after each of thermal treatment
Simulation Studies One of the most difficult yet important aspects of TCAD simulation is proper calibration of TCAD tool with respect to the foundry. The difficulty arises from the large number of variables that can be adjusted in the simulator. Many discrepancies between experimental and simulation results can be resolved by proper understanding of the limitations of the simulators. In particular, the grid, boundary conditions, and the various models, all of which are user-selectable, can have a dramatic impact on the simulation results. The various aspects of grid selection, boundary conditions and model coefficient values were taken into account while comparing the simulation results with the experimental values. Process simulations have been carried out for designing process for shallow junction depth at BEL. The simulated process flow is being implemented at BEL for detector optimization for charged particle spectroscopy applications. The cross-section of the simulated device showing different layers and contour for the junction depth Doping Profile after each of thermal treatment

29 Silicon Detectors with Inbuilt JFET Simulation Studies & Design
An extension of PIN diode development work Fabrication of JFET along with PIN diode detector avoids stray capacitances and micro phonic noise pickups SDD is based on the lateral charge transport scheme. The signal charge generated by radiation is collected by a small area anode (small capacitance≈ 0.1pF). The capacitance of the detector is independent of the detector area These detectors can be cooled down to -20ºC that would give energy resolution of ≈180 eV ( PIN diodes) and ≈150 eV (SDD) In the last decades several new silicon detector have been developed for physics experiments and for x-ray imaging in biomedical imaging. With experience gained, we are initiating this activity to develop systems for HEP and Industrial users. We have carried out simulation in detail for the development of SDD.

30 Radial Cross Section of SDD & JFET
Based on the published data, we have carried out the simulation with the calibrated simulators used in earlier PIPS program

31 Process Simulations Fabrication of the proposed detectors require 10 Masks layers Back plane alignment needed Process simulations for fabrication of the detectors have been carried out and implant energy, dose values and temperature cycles have been studied Starting substrate : 4 KΩ-cm P-well : 1E12 80 KeV N-channel : 8E12 80 KeV P+ Gate :1E14 60 KeV N+ Source & Drain :1E15 80 KeV The temperature cycles are C Long annealing temperature cycle to recover the bulk carrier life time. PIPS process is simpler only fivce masks are involved but in SDD it is nearly nine mask processes. These processes are available at BEL where we are planning to carryout the R&D and process optimisation

32 Radius=1.2 mm Dia = 2.4 mm Area = 4.5 mm2 Chip will be around 1 cm2 Resistor, L=50, W=40, resistance value=600 K



35 N-JFET Characteristics
Cgs=0.2 pF Cgd=0.2 pF Gate curr=0.2 pA

36 Silicon Drift Detector with Integrated Front-end electronics
Low noise operation with large active area Energy and position sensing capability High energy resolution ~150eV High position resolution ~ 11 m High count rate capability 2e6 cps/cm2 Applications of Silicon drift detectors X-ray & -ray Spectroscopy Simulation studies for SDD and inbuilt JFET completed Analog X-ray AcquisitionSystem (AXAS)

37 CMOS ASIC from SCL Concept to CHIP
Full custom designs DETECTOR(S) FRONT END DOSIMETER ASIC. CODA OCTAL Charge Preamp OCTPREM Four low noise ASIC are undergoing tests. The prileminary results show about electron noise in our CMOS charge amplifiers For different applications the dynamic range is different and detector capacitance is different and therefore we variety of ASIC,s 8 CHANNEL SILICON STRIP PULSE PROCESSOR. SPAIR 8 CHANNEL CURRENT PULSE PREAMPLIFIER MICON

38 The preamplifier FOR OCTPREM

39 Block Diagram “SPAIR”

40 MICON Error amp out I to V &SHAPER/ Buffer bias in ref KEY FEATURES

41 The process technology for large area silicon detectors has been successfully developed and silicon strip detectors meeting all the electrical and technological specifications for it’s qualification as preshower sensors have been produced The leakage current in detectors is around 2-5 nA/cm2 and breakdown voltage is in excess of 500V The approach of employing gettering techniques during fabrication has sustained the bulk effective carrier lifetime to high value > 10 ms The injection of carriers from the back plane at full depletion voltage which was the major problem for high voltage operation of the detectors has been effectively tackled by incorporating double implantation at back side so as to have thicker and uniform n+ layer the strip detectors that show high leakage current in strips can become usable detectors with one of the Guard Rings grounded Guardring collects most of the signal charge generated close to or outside of the active area avoiding the number of interactions in which imperfect or incomplete charge collection would occur. Simulation studies for designing Silicon Drift Detector with integrated N-JFET have been done and results are presented The small area silicon diode detectors that have been produced as spin offs of the strip detector fabrication process have been evaluated and they show excellent static and performance characteristics. These diode detectors have given energy resolution of 2.8 KeV for 60 KeV γ-rays and 45 to 50 KeV for 5 MeV α particles [6]. These PIN diode detectors have been packaged for use in various applications like low energy X-ray spectroscopy, α-spectroscopy, dosimetry, area monitoring etc in BARC and are also made commercially available at BEL for other labs.

42 Preshower Readout Architecture
The transparency shows the readout architecture of the preshower. The front-end electronics shown within dotted lines is incorporated on motherboards and installed in the CMS detector. The micromodules having Si strip detectors and front-end electronics in the form of ASIC called PACE are mounted on the motherboards. The DDU and FEC modules are installed in the counting room. We have developed Si strip detector and have undertaken its production. We have also contributed in development of front-end ASICs on the preshower motherboard called PACE and the K chip. We have made the draft specifications of the DDU and have begun work on its design using the DCC board.

43 DDU Functional Requirements
Optical to electrical conversion & de-serialization of incoming data streams Integrity verification of incoming data packets/event fragments Data reformatting Data reduction DDU event formation Transmission of DDU events to the global DAQ through the S-Link64 interface Transmission of spying events to the local DAQ through VME interface

44 DDU Input Data Format

45 Data Processing in DDU Pedestal Subtraction
Common mode noise Subtraction Threshold Comparison Synchronization Check Deconvolution α = Y1 v0 β = Y1 v1 + Y2 v0 γ = Y1 v2 + Y2 v1 + Y3 v0 Charge Extraction Q = W1 v1 + W2 v2 Data concentration and output formatting

46 DDU Output Data Format Header _BOE: Begin Of Event 4 bits
_FOV FOrmat Version 4 bits _LV1_id Trigger Number 24 bits _BX_id Bunch Number 12 bits _Source_id Source Id 12 bits _Evt_ty Event Type 4 bits Trailer _Evt_lgth Event size in 64 bit words 24 bits _Evt_stat Event status 8 bits Integrity CRC 16 bits

47 Data Concentrator Card (DCC)

48 DDU Architecture in DCC
iFIFO nFIFO Data Processor 9 x Vertex2Pro Data Concentrator VME64 Interface FIFO Multiplexer S-Link-64 Interface 68 1 oFIFO 8 x links To CMS DAQ From SMB VME64 bus

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