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

readout

Atsuhiko OchiKobe University

9th RD51 meeting @ CERN21st February, 2012

A. Ochi 9th RD51 meeting

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.

Requirements for more stability

21 Feb 2012

A. Ochi 9th RD51 meeting

First trial: m-PIC with resistive overcoat 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

R

RR

+HV

100mm

25mm

CathodeResistive sheet

Anode 400mm

Drift plane-HV

~1cmDetection area: filled by gas

25μm

25μm

Anode

Resistivefilm

Cathode

E-field will be dropped by spark current.

21 Feb 2012

A. Ochi 9th RD51 meeting

Setup for first prototype Vd = 2kV (2kV/cm) Vac = 500 – 620V Gas: Ar+C2H6 = 1:1 10cm x 10cm

10cm

400mm

21 Feb 2012

Improvements for production

10cm

First prototypeSparks on cracks

4th prototype

Cracks are on substrate

No crack, but bad quality

5th prototype

Qualities aregetting better

A. Ochi 9th RD51 meeting

Signal can be found, but slightly improvements for stability was found.

21 Feb 2012

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

A. Ochi 9th RD51 meeting

First resistive m-PIC

New resistive m-PIC

Connect to one pad

R+HV(~500V)

R(0V)

Capacitive readoutFor second coordination

21 Feb 2012

A) Start from PI film with cupper layer

B) Nickel plating on top

C) Double side photo exposure

D) Double side etching

E) PI etching from bottom

F) Cu pattern etching (second coordinate)

Prototype production processfor new resistive m-PIC (Raytech inc.)

A. Ochi 9th RD51 meeting

Polyimide (25mm)

Cupper

Ni

Photo mask

21 Feb 2012

SPB (50um)

G) Anode post plating with Nickel

H) Surface etching ( cathode pattern )

I) Resistive polyimide coating and baking

J) Grinding a surface resistive polyimide and attaching bottom substrate

Production process (cont’d)

A. Ochi 9th RD51 meeting

PI (50um)

21 Feb 2012

K) Making holes from bottom using laser drilling

L) Hole plating after Cu spatter

M) Etching the surface metal. Top of anodes and resistive cathodes are remained on surface.

Production process (cont’d)

A. Ochi 9th RD51 meeting 21 Feb 2012

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

Surface picture of a prototype

A. Ochi 9th RD51 meeting 21 Feb 2012

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.)

Operation tests (very2 preliminary)

A. Ochi 9th RD51 meeting

590 600 610 620 630 640 650 660 670 6801000

10000

GainExponential (Gain)

Anode Voltage

Gain

(with

55F

e)

Cathode signals

21 Feb 2012

(Trigger from anode signals)

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.

Problems

A. Ochi 9th RD51 meeting

Parasite hole

21 Feb 2012

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

Summary and future prospects

A. Ochi 9th RD51 meeting

(0V)

R+HV(~500V)

New resistive m-PIC-HV(~-500V)

Direct connection to readout

21 Feb 2012