Micro Pixel Chamber ( m -PIC) with resistive cathode & capacitive readout

1. Micro Pixel Chamber (m-PIC) with resistive cathode & capacitive readout Atsuhiko Ochi Kobe University 9th RD51 meeting @ CERN 21st February, 2012

2. Requirements for more stability • The m-PIC is now quite stable • By improvement of the production • However, more stabilities and robustness is needed for some application • Operation in heavy ionized particle • Very high gain for detecting single electron •  The electron density may excess the Raether limit(107-8) • Continuous sparks will destroy the electrodes easily because of existence of substrates near electrodes. • Dead time due to resuming HV is also problem. • For muon detector in the LHC (HL-LHC) detector, those stability studies are very important! • There are two approaches for stable operation • Reducingthe spark • Making spark tolerant structure • New Idea • Self quench mechanism for sparks will be added, using MPGD (m-PIC) electrodes • 1st trial: Metal cathodes are covered by high resistivity material. • This report: Cathodes are made from resistive material, and cathode signals are read using induced charge. A. Ochi 9th RD51 meeting

3. First trial: m-PIC with resistive overcoat Drift plane -HV E-field will be dropped by spark current. • Resistive kapton is on the cathodes of m-PIC. • Large current from spark reduce the e-field, and spark will be quenched. • Huge signal beyond the “Raether limit” will also be suppressed • Signal from low energy deposit will observed with higher gas gain • This design provide one promising possibility of MIP detector under hadronic background 25μm ~1cm Detection area : filled by gas 25μm Resistive film Cathode Resistive sheet Cathode 25mm Anode +HV 100mm Anode 400mm R R R A. Ochi 9th RD51 meeting

4. Setup for first prototype • Vd = 2kV (2kV/cm) • Vac = 500 – 620V • Gas: Ar+C2H6 = 1:1 • 10cm x 10cm 10cm 400mm A. Ochi 9th RD51 meeting

5. Improvements for production Sparks on cracks First prototype Cracks are on substrate 4th prototype 5th prototype 10cm No crack, but bad quality Qualities are getting better Signal can be found, but slightly improvements for stability was found. A. Ochi 9th RD51 meeting

6. Remnant problems and new design • Sparks are still occurred on resistive m-PIC • More precise manufacturing are needed • Problems for alignment of anode and cathode position •  Dual page mask + liquid resistive capton • Dual page mask  Both anodes and cathode images are printed simultaneously • To make higher resistivity between anodes and cathodes • New structure using capacitive readout from cathodes.(Thanks to R. Olivaira) • Spark will be suppressed more strong First resistive m-PIC +HV(~500V) R (0V) Capacitive readout For second coordination New resistive m-PIC R Connect to one pad A. Ochi 9th RD51 meeting

7. Prototype production processfor new resistive m-PIC (Raytechinc.) Cupper • Start from PI film with cupper layer • Nickel plating on top • Double side photo exposure • Double side etching • PI etching from bottom • Cu pattern etching (second coordinate) Polyimide (25mm) Ni Photo mask A. Ochi 9th RD51 meeting

8. Production process (cont’d) • Anode post plating with Nickel • Surface etching ( cathode pattern ) • Resistive polyimide coating and baking • Grinding a surface resistive polyimide and attaching bottom substrate SPB (50um) PI (50um) A. Ochi 9th RD51 meeting

9. Production process (cont’d) • Making holes from bottom using laser drilling • Hole plating after Cu spatter • Etching the surface metal. Top of anodes and resistive cathodes are remained on surface. A. Ochi 9th RD51 meeting

10. Surface picture of a prototype • Delivered at 8th Feb, 2012 from Raytech • This is second trial for capacitive readout • Anode pixel is well aligned at center of cathode • 10cm x 10cm (400 micron pitch) has been produced • Two samples were produced • Surface resistivity (mean of all surface) : • 0.7MW • 1.2MW A. Ochi 9th RD51 meeting

11. Operation tests (very2 preliminary) • Only one of two sample provides signals using 55Fe. • Gas: Ar+C2H6 = 7:3 • Sparks are found because of parasite holes of anode pixels. (next slide.) Cathode signals (Trigger from anode signals) A. Ochi 9th RD51 meeting

12. Problems Parasite hole • There found parasite holes … • Laser drilling for anode pixels are not in right place due to deformation of the substrate. • At the surface resistive polyimide baking. • We need more improvements of process. A. Ochi 9th RD51 meeting

13. Summary and future prospects • m-PIC with resistive cathodes and capacitive readout is newly developed. • We confirmed a operation principly • The 55Fe signals are read from both anodes and capacitive readouts. • There remain some problems in production process. • To improve the quality of production, we are considering following methods • Changing surface resistive materials • Some other organic material, or very thin metal layer, without baking for fixing it. • Considering the process for making • New operation condition with applying HV to resistive cathode • There are no HV on anode  No coupling capacitor is needed for anode readout -HV(~-500V) (0V) New resistive m-PIC Direct connection to readout +HV(~500V) R A. Ochi 9th RD51 meeting