Development of PIC with resistive electrodes using sputtered

Development of μ-PIC with resistive electrodes using sputtered carbon Kobe Univ. , Tokyo ICEPPA F. Yamane, A. Ochi, Y. Homma S. Yamauchi, N. Nagasaka, H. Hasegawa, T. Kawamoto. A, Y. Kataoka. A, T. Masubuchi. A, 15/10/2015 p p p Outline Introduction New resistive material Pixel alignment Gain measurement Summery and further prospects MPGD 2015@Trieste 1

ü Introduction p New resistive material p Pixel alignment p Gain measurement p Summery and further prospects 15/10/2015 MPGD 2015@Trieste 2

Micro Pixel Chamber: μ-PIC • 2 D gaseous imaging detector produced by PCB technology. • For many purpose. . . Dark Matter Search(NEWAGE) K. Nakamura PTEP (2015) 043 F 01 Talked by T. Ikeda(15/10) ETCC(Electron-Tracking Compton Camera) T. Tanimori+ The Astrophysical Journal 810 (2015) Talked by T. Takemura(14/10) and more application… 15/10/2015 Mascot of NEWAGE "Daakumatan" A. Ochi+ NIM A 471 (2001) 264 Space Dosimeter(PS-TEPC) Y. Kishimoto NIM A 732 (2013) 591 MPGD 2015@Trieste Neutron Imaging J. D. Parker+ NIM A 697 (2013) 23 3

Our purpose l Stable operation in high rate HIPs(Highly Ionizing Particles) environment ->μ-PIC needs to have spark tolerant l In this research Ø We propose μ-PIC for ATLAS forward muon detector. Ø Sputtered carbon is used as resistive cathodes for spark protection. Ø The production improvement and fundamental measurement of resistive μ-PIC are reported. 15/10/2015 MPGD 2015@Trieste 4

Physics motivation l Muon Tagger • ATLAS new endcap forward muon detector considered to be installed nearby the beam line (2. 7<|η|<4. 0 ) after the long shutdown from 2023. l Very hard environment for detectors • Multiple track are incident in very small area. • High rate HIPs background ~100 k. Hz/cm 2. • Detector size is limited (<5 cm thickness). l Requirements for Muon Tagger Ø Granularity of ~100 um for track separation. Ø Stable operation with high gain in high rate HIPs. Ø Thickness<5 cm 15/10/2015 MPGD 2015@Trieste 5

Why μ-PIC ? l Properties Ø Good position resolution(2 D) & high rate capability. • Isolated pixels are arranged by 400 um pitch with 250 um diameter hole. • Each pixel has an anode pin and a surrounding cathode. • 2 D readout by orthogonal anode/cathode strips without the loss of signals. Ø μ-PIC has no floating structures (wire, foil, mesh…). • Made by PCB/FPC technology. • Large detector(30 cm) can be produced. • Larger area available by arranging many μ-PIC to tile form. (It is possible because there is no flowing structure) l μ-PIC with resistive electrodes was developed for spark protection. (Next slide) 15/10/2015 MPGD 2015@Trieste 10~ 30 cm μ-PIC μ-PIC μ-PIC 6

μ-PIC with resistive cathode l Resistive cathodes for reducing sparks • Strong spark reduction was shown at high gain(>10000) operation under irradiation of the fast neutron(a few Me. V). • Spark rate was 104 times less than normal μ-PIC Spark rate = Spark counts / Number of neutron l Capacitive readout without AC coupling • Pickup electrodes are lying under resistive cathodes and insulator(polyimide). • Charges are induced from resistive cathodes. • This capacitive readout can be applied for anodes. • Detector construction can be simplified. 15/10/2015 MPGD 2015@Trieste 7

Requirements l Requirements Ø Granularity of ~100 um • The pixel pitch should be reduced (400 um->100 um). ->Resistive ccathodes are needed to be able to form precise pattern. Ø Stable operation • High resistivity: Strong tolerance for sparks but continuous voltage drop distort electric field • Low resistivity: Sparks cannot be reduced. • It is important that resistivity must not be too high and too low. ->Fine resistivity control is needed. Ø Detector size • No floating structure & capacitive readout -> Possible! l Previous resistive material: Carbon polyimide • Cathode surface is not flat so much. • Difficult to form more precise pattern. • Fine resistivity control is difficult. 300 um l Other resistive material is needed to achieve requirements. 15/10/2015 MPGD 2015@Trieste 8

p Introduction ü New resistive material p Pixel alignment p Gain measurement p Summery and further prospects 15/10/2015 MPGD 2015@Trieste 9

New material for resistive electrodes l Sputtered carbon has been developed and studied in Kobe Univ. (2013~). • Diamond like carbon is formed on the substrate • Very precise pattern can be formed easily with lift off process 3 D image of resistive μ-PIC Left: Carbon polyimide, Right: Sputtered carbon 300 um 15/10/2015 MPGD 2015@Trieste 10

Properties of the sputtered carbon ü Fine and uniform pattern. • Enough to achieve granularity of ~100 um. ü Wide range of resistivity control is available　 (50 kΩ/sq. ~3000 MΩ/sq. ). • Thickness control • Nitrogen doping ü Uniform resistivity. ü Strong attachment on substrate. ü Large size available (>2 m) Vacuum chamber (with Ar + N 2 gas) Be-Sputter Co. Ltd. (Kyoto Japan) Sample Rotating drum 4. 5 m round Sputtering target Surface Resistivity[MΩ/sq. ] 10000 A resistive strips foil for ATLAS NSW 15/10/2015 Resistivity vs thickness Pure C 1000 DLC 100 40 min. 10 N-DLC 3 hours 1 N 2 content in Ar is 3. 2% 0. 1 0. 01 100 MPGD 2015@Trieste 1000 Thickness [Ǻ] 10000 11

p Introduction p New resistive material ü Pixel alignment p Gain measurement p Summery and further prospects 15/10/2015 MPGD 2015@Trieste 12

Alignment problem l Anode pins are formed by 2 different processes on “Top substrate” and “Under substrate” (next slide). l Sometimes, there are misalignments of pixels. . . ->Anode pins contact to the inner pickup electrodes! l Alignment process should be improved! Top substrate Under substrate Misaligned under anode pin Top anode pin Misalignment of anode 15/10/2015 MPGD 2015@Trieste 13

Previous production method Manufactured by Raytech Inc. Cathode pattern Pickup electrode ① ② ③ ④ ⑤ Cathode pattern Top anode pin Pickup electrode 25 um Top substrate: Polyimide 25 um Cathode patterning using double side mask Cu plating on top surface Etching substrate Plating for anode pin 15/10/2015 MPGD 2015@Trieste 14

Previous production method Manufactured by Raytech Inc. Cathode pattern Pickup electrode Cathode pattern Top anode pin Pickup electrode 25 um ① ② ③ ④ ⑤ ⑥ Top substrate: Polyimide 25 um Cathode patterning using double side mask Cu plating on top surface Etching substrate Plating for anode pin Under substrate: Polyimide Because the surface is covered by Cu that will become anode strips, the anode pin of top surface cannot be seen… ⑦ Etching substrate and plating for anode pin -> Misalignment! 15/10/2015 MPGD 2015@Trieste 15

Improved production Manufactured by Raytech Inc. Cathode pattern Pickup electrode Cathode pattern Top anode pin Pickup electrode 25 um 75 um Dry resist ① Under substrate: Transparent dry resist 75 um ② Exposure 15/10/2015 MPGD 2015@Trieste 16

Improved production Manufactured by Raytech Inc. Cathode pattern Pickup electrode Dry resist ① ② ③ ④ ⑤ Cathode pattern Top anode pin Pickup electrode 25 um 75 um Cu sputtering for anode connection Under substrate: Transparent dry resist 75 um Exposure Developing Cu sputtering for anode connection Ni plating 15/10/2015 MPGD 2015@Trieste 17

Improved production Cathode: Sputtered carbon Pickup electrode Top anode pin Pickup electrode 25 um 75 um ① ② ③ ④ ⑤ Under substrate: Transparent dry resist 75 um Photo etching for anode pin. Cu sputtering for anode connection Ni plating Carbon sputtering with lift off 15/10/2015 MPGD 2015@Trieste 18

μ-PIC(RC 33) Ø Ø Readout pitch: 400 um Active area: 10 cm× 10 cm, 256 strips Pixels are well aligned in all region. Carbon sputtered cathodes are well formed. 250 um 15/10/2015 MPGD 2015@Trieste 19

p Introduction p New resistive material p Pixel alignment ü Gain measurement p Summery and further prospects 15/10/2015 MPGD 2015@Trieste 20

Gain curve l Gas gain measurement using 55 Fe source • Gas mixture: Ar: C 2 H 6 = 90: 10 • Drift field: 2 k. V/cm • Cathode HV: -500 V ~ -700 V • Anode: Ground 999999 • Readout: Cathode pickup electrode • Preamp: ASD ü Gain of more than 10000 was achieved. ü There were no discharges. Gain curve Gain FWHM: 19% 999999 l However, there are some problems… • Signals cannot be read by Anode. • Gaseous amplification was not observed in Anode HV & Cathode ground operation (conventional way). • Compared to previous detector, - Operation HV is higher than about 100 V. - Gain increases slowly with HV value. • Something is wrong! 15/10/2015 RC 33 -1 RC 33 -3 400 450 500 550 600 HV [-V] 650 700 750 Anode signals cannot be seen MPGD 2015@Trieste Cathode signal Gain of old μ-PIC with carbon polyimide 21

The cause of problems l Disconnection between anode pins and anode strips. • It is thought that anode connection by Cu sputtering was incomplete because under substrate was thick (75 um). Cathode –HV & Anode Ground operation only available. l Gain reduction was seen because of charge up on anode pins. Gain variation Electrons remain on anode pin 0 -HV 10000 Gain -HV 1000 100 450 500 550 Within 10 min after source on 15/10/2015 MPGD 2015@Trieste 600 650 HV [-V] 700 750 800 More than 2 hours after source on 22 850

p Introduction p New resistive material p Production p Gain measurement ü Summery and further prospects 15/10/2015 MPGD 2015@Trieste 23

Summary and further prospects l Summary ü μ-PIC with resistive cathode using sputtered carbon is developed. ü Thanks to production improvement, pixels were well aligned in all active region(10 cm× 10 cm). ü Gain of more than 10000 was achieved with no discharge. (Ar: C 2 H 6=90: 10) ü Connection between the anode strip and the anode pin is incomplete. l Further prospects ü ü ü Anode connection should be improved (now producing). Spark torrent test of carbon sputtered μ-PIC (3/2016). E-field simulation. Reducing pixel pitch. 400 um -> 200 um True 2 D readout with SRS system. 15/10/2015 MPGD 2015@Trieste 24

Thank you! 15/10/2015 MPGD 2015@Trieste 25