e + e - Collider Detector R&D

June 6, 2001 US Japan Meeting

e+ e- Collider Detector R&D

Status Report to US Japan Committee

Daniel Marlow Princeton University

June 5, 2001


Projects and Participants• Radiation hard readout for the Silicon Vertex Detectors

– Hawaii, KEK, Princeton, Tokyo

• Resistive Plate Chamber R&D– KEK, Oregon, Princeton, SLAC, Tohoku

• Vertex Detector R&D– Hawaii, KEK, Tokyo


The SVD Readout Chip: the VA1

• 128 channels

• Descendent of Viking (O. Toker et al., NIM A340 (1994) 572.)

• AMS 1.2 um CMOS

• Noise:

timeshaping s 2 @

pF/ 1.6 165 ENC

ee


New Directions

• Incorporation of a fast trigger output.

• Implementation in a sub-micron CMOS process to attain radiation hardness.


Radiation Damage in MOS Transistors

xE

depends on ionization

2ox

0

ox

t

xdx

xdEV

t

th

Reducing the oxide thickness by half is equivalent to cutting the dose by four.


Process Comparison

In the range of interest to BELLE, the noise vs. dose performance dramatically improves with decreasing feature size, as expected.


Indeed, the 0.35-um process exhibits phenomenal radiation hardness.


Single Event Phenomena

Although the submicron processes appear to offer a total dose resistance that is considerably better than needed, one still needs to worry about “upsets” induced by ionization that is highly localized in space and time. This is our current focus.


Single Event Upset and Latch-up• Single event upset (SEU)

– Flip-flops flip when they should flop.

• Single event latch-up (SELU)– Parasitic conduction paths form in the IC’s substrate.

– Current draws large enough to destroy the chip through Joule heating can occur.

• It is not clear how these effects will vary with feature size. Experimental measurements are needed.


SELU Mitigation

• According to the AMS measurements, the addition of an epitaxial layer during fabrication should improve the latchup performance of the VA1 chips.

• We are refabricating the VA1 chip in the AMS 0.35 um CMOS with an epitaxial layer added.


SEU Mitigation

• The logic design of the VA1TA will incorporate 2 of 3 majority logic to detect and automatically correct SEU-induced errors.


SEU, SELU, and the VA1

• Despite these precautions, it is important that we understand the effects.

• We thus plan to carry out systematic comparisons between VA1’s implemented with varying line widths (and with & without an epitaxial layer).

• IDEAS has submited two major engineering runs: – VA1 to AMS 0.35 m with epitaxial layer.

– VA1TA to AMS 0.35 m with epitaxial layer.


RPC Principles of Operation

A passing charged particle induces an avalanche, which develops into a spark. The discharge is quenched when all of the locally ( ) available charge is consumed.

2cm 1.0r

Spacers

Signal pickup (x) India Ink

Resistive plates 8 kV

Signal pickup (y) India Ink

+++++++++++++++_ _ _ _ _ _ _ _ _ _ _

+++ +++++_ _ _ _ _ _ _The discharged area recharges slowly through

the high-resistivity glass plates.

Before

After


RPCs are not robust.Dark currents arising from surface defects can cause a loss of efficiency. In the early days of Belle, serious efficiency losses were observed.

Fortunately, these problems were resolved, but similar problems continue to plague the BaBar RPCs.

Belle


The RPC Death Spiral

High dark currents induce a IR voltage drop across the resistive plates, which lowers the voltage across the gap, causing the chamber to slide off the efficiency plateau.

Increasing the applied voltage doesn’t help since it merely results in increased dark current.


Surface Defects in the Babar RPCs

Work by J. Va’vra and H. Band of BaBar has shown that the linseed oil surfaces have suffered damage.


Irreversible Current Increases Due to Stalagmite Formation


Resistivity of Linseed Oil

It appears that the linseed oil is not fully polymerized, which leaves it with a low resistance.

Data from C. Lu (Princeton/BaBar)


Oxygen Treatment

1000 3000 5000 7000

HV (V)

0

20

40

60

80

I (A

)

before flow N2/O2after first 5 days flowing N2/O2after another 10 days flowing N2/O2

BaBar RPC gas Ar/Isobutane/R134A (60/4.6/30.4)

C. Lu at Princeton (BaBar) found that oxygen causes the linseed oil to polymerize, which raises its resistivity and lowers the dark current.

Before5 days N2/O2

15 days N2/O2

Data from C. Lu (Princeton/BaBar)


Is Oxygen a Long-Term Cure?Efficiency vs. Time

Region Before Treatment

After 5 days dry air

8 days later

8 days dry air

7 days later

29 days later

Worst

Area

83.1% 94.0% 89.7% 96.0% 88.5% 82.3%

Best Area

90.6% 95.4% 94.7% 94.0% 94.0% 95.0%

Full-chamber Average

83.9% 93.6% 90.7% 95.5% 92.0% 90.5%

Data from C. Lu (Princeton). Obtained using RPC extracted from BaBar.


Pixel Detector R&D• Areas of study include bump-bonding studies & electronics development.

• Original vendor list included GEC Marconi (Britain) and Advanced Interconnect Technology (AIT Hong Kong).

• Marconi withdrew, so that bumps were pursued with AIT.

• Test samples were 20 x 40 arrays of 50 x 100 µm2 pixels.

• Both “thick” (300 µm) and “thin” (100 µm) sensors were bonded to dummy readout chips were bonded.


Sample Test Bonds

Optical ImageSEM Image


IR Images

Good bonds

Overpressed bonds

IR images were used to examine the bonds, instead of the x-ray technique used by ATLAS.

To our knowledge, this is the first time that 100 µm-thick wafers have been successfully bump bonded in HEP.


Summary

• Development of SVD radiation-hard electronics is proceeding smoothly.

• RPC studies are showing some interesting effects, but a clear solution to the bakelite RPC efficiency-loss problem is not fully in hand.

• There are some promising results on thin-pixel detector bump bonding, but much remains to be done.

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e + e - Collider Detector R&D