1. Atsuhiko Ochi Kobe University
Micro Pixel Chamber (m-PIC) with resistive cathode & capacitive readout
Atsuhiko Ochi
Kobe University
9th RD51 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
Reducing the 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
21 Feb 2012

3. First trial: m-PIC with resistive overcoat
+HV
100mm
25mm
Cathode
Resistive sheet
Anode
400mm
Drift plane
-HV
~1cm
Detection area
: filled by gas
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
Anode
Resistive
film
Cathode
E-field will be dropped by spark current.
A. Ochi 9th RD51 meeting
21 Feb 2012

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
21 Feb 2012

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
21 Feb 2012

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
Connect to one pad
First resistive m-PIC
+HV(~500V) R
(0V)
Capacitive readout
For second coordination
New resistive m-PIC R
A. Ochi 9th RD51 meeting
21 Feb 2012

7. Prototype production process for new resistive m-PIC (Raytech inc.)
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
21 Feb 2012

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
21 Feb 2012

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
21 Feb 2012

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
21 Feb 2012

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
21 Feb 2012

12. Problems 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.
Parasite hole
A. Ochi 9th RD51 meeting
21 Feb 2012

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
(0V)
-HV(~-500V)
New resistive m-PIC
Direct connection to readout
+HV(~500V) R
A. Ochi 9th RD51 meeting
21 Feb 2012