MCP Electrodes and End Spoiling

Jeffrey Elam, Qing Peng, Anil Mane, Thomas Prolier, Joe LiberaArgonne National LaboratoryLarge Area Photodetector Collaboration MeetingOctober 15, 2009

MCP Structure

2

1) resistive coating (ALD)2) emissive coating (ALD)3) conductive coating (thermal

evaporation or sputtering)

pore

Sputtering system

Deposition chamber Load lock Sample transfer Arm

Sample rotation

RF Magnetron Sputtering System, AJA International ATC 2400John Pearson, MSD

Uncoated MCP

MCP100nm AZO

MCP+100nm AZO+Cr 5nm+Au 50nm

RF Magnetron Sputtering on Au/Cr Electrodes

We’re done, right?

No.

Electrodes and End-Spoiling in MCPs

b

Endspoiling: h=b/d

IEEE Trans Nucl. Sci. 19 (3) 74-84 1972 End spoiling output side:• increases spatial resolution• decreases gain• trade-off: h~1-2

Input side:• h~0.5-0.8

Importance of End Spoiling

A

AB

B(end spoiling)

• N(E) becomes more narrow as end spoiling increases

Effect of End Spoiling on Electron Energy Distribution

Effect of End Spoiling on Electron Energy Distribution

• N(E) narrows as end spoiling increases

Simulations:

h=0

h=0.5

h=1

h=3

• small increase in spatial resolution (10%) with 1.5 end-spoiling

Effect of End Spoiling on MCP Spatial Resolution

Effect of End Spoiling on MCP Spatial Resolution

• No systematic change in angle distribution with end-spoiling

Simulations:

h=0 h=0.5 h=1 h=3

Effect of End-Spoiling on MCP Gain

Gain ~ (SEC) (L/z)

SEC=secondary electron coefficientL=pore lengthz=distance between collisions

Since E field gradient=0 in electrode length h, no gain there

Gain ~ (SEC) (L/z) exp(-0.65h)

• Gain decreases with end-spoiling

IEEE Trans Nucl. Sci. 19 (3) 74-84 1972

Effect of End-Spoiling on MCP Gain

h=1.2

h=2.2

h=3

h=4

• Gain decreases with end-spoiling

Gai

n100

10

1

0.1

0.01

Voltage

13

Controlling End-Spoiling

RF-magnetron sputteredTi and Cu in high aspect ratio trench

http://www.electroiq.com

• Sputtering is not “line-of-site”• Need to use evaporation

Controlling End-Spoiling

• h=atan(θ)

Electrode Materials

Ni 72%Cr ~17%Fe ~10%Mn ~1%

Inconel 600: Trademark of Special Metals Corporation

metal melting Point°C

Resistivity µΩ cm

thermal conductivity

W/mK

VickersHardness

MPa

Adhesion Oxidation Resistance

Price to coat 8” square ($)

Inconel 600 1400 104 15 638 Great OK $0.3

Gold 1064 2.2 318 216 Terrible Best $6

Copper 1084 1.7 401 369 Poor Poor $0.06

Ossy suggests: 200 nm Inconel 600, h=1-2.

Ni ~80%Cr ~20%

Nichrome:Brand name, range of

compositions

Thermal Evaporation System, BOC Edwards AUTO 306Hau Wang, MSD

Thermal Evaporation System, BOC Edwards AUTO 306Hau Wang, MSD

~200nm thermal evaporatedNiCr on 33 mm ALD MCP

(end-spoiling not controlled)

sample rotation motor