brookhaven science associates u.s. department of energy multi-element silicon detectors for x-ray...

$: Brookhaven Science Associates U.S. Department of Energy Multi-element Silicon Detectors for X-ray Spectroscopy and Diffraction D. P. Siddons, A. Kuczewski$
Brookhaven Science AssociatesU.S. Department of Energy

Multi-element Silicon Detectors for X-ray Spectroscopy and Diffraction

D. P. Siddons, A. KuczewskiNational Synchrotron Light Source,

P. O'Connor, G. De Geronimo, Z. LiInstrumentation Division,

Brookhaven National Laboratory,

Upton NY 11973


BNL Collaborators for silicon detector development

Zheng Li , Pavel Rehak, Wei Chen, Rolf Beuttenmuller, detector elements (Inst. Div.).

Paul O'Connor, Gianluigi De Geronimo, ASIC design (Inst. Div). Peter Siddons, Tony Kuczewski, computer and user interface

(NSLS) Technical assistance:

John Triolo, Don Pinelli (Inst.) , Denis Poshka, Tony Lenhard, Shu Cheung, Rick Greene (NSLS)


Outline

The HERMES ASIC design performance

Embedded EPICS IOC EPICS & RTEMS nslsdet record

Examples Powder diffraction GISAXS

Next step


Typical fluorescence EXAFS spectroscopy geometry

Sample

Sensor Detector

Resolution : > 200 S/N < 300 eV FWHM

Rate : > 10 MHz/cm2

> 100 kHz/pixel

Spectroscopy (energy windows)

Electronics front-end processing readout

2 – 20 keV


Optimum pixellation

10 100 1k100

1k

10k

12

118

1182

400

P = 3W, p2 = 5mW

L = 20mm

cpa

= 400fF/mm2, c

pf = 75fF/mm

Ci = 300fF

p2 = 4mW

Rate = 10MHz

40MHz

Rm

s el

ectr

ons

F

WH

MS

i [eV

]

Pixel count N


'HERMES' ASIC channel overview

5 mW 3 mWASIC

continuous reset

INPUT p-MOSFET•optimized for operating region•NIM A480, p.713

CONTINUOUS RESET•feedback MOSFET•self adaptive 1pA - 100pA•low noise < 3.5e- rms @ 1µs•highly linear < 0.2% FS•US patent 5,793,254•NIM A421, p.322•TNS 47, p.1458

counters

discriminators

DACS

DISCRIMINATORS•five comparators•1 threshold + 2 windows•four 6-bit DACs (1.6mV step)•dispersion (adj) < 2.5e- rms

COUNTERS•three (one per discriminator)•24-bit each

baseline stabilizer

HIGH ORDER SHAPER•amplifier with passive feedback •5th order complex semigaussian•2.6x better resolution vs 2nd order•TNS 47, p.1857

BASELINE STABILIZER (BLH)•low-frequency feedback, BGR•slew-rate limited follower•DC and high-rate stabilization•dispersion < 3mV rms•stability <2mV rms @ rttp<0.1•TNS 47, p.818

high-ordershaper


charge preamplifier shaper with BLH discriminators and DACs counters

32 channels, 3.6 6.3 mm2

'HERMES' ASIC photo


direct wire bonding

bump bonding

integrated metal lines

strips

Interconnecting pixel to front-end electronics

ASIC

sensor

+ interconnect parasitic+ bond length- fringe capacitance- charge sharing and trapping

ASIC

sensor

+ interconnect parasitic- constraint on ASIC area and layout- fluorescence from Pb (Sn/Pb/Ag)- illumination from segmented side

ASIC

sensor

+ dielectric losses interconnect parasitic- bond length

+ bond length- interconnect parasitic- dielectric losses

ASIC

sensor

6mm10µm, Si3N4 (r=6.5,tan() 1m), 3µm, Ci1.2pFFWHMloss= 8.5/q·(2kTCitan()) 180eV

INTERCONNECT


One quadrant with ASICS

96 pads wire-bonded to 3 ASICS.

The long bonds are rather fragile, but this approach provided least parasitic capacitance.

Each ASIC provides 32 channels of low-noise analog/digital processing.

ASIC appears to have 100% yield (no bad channels to date).


Backscattering geometry for microprobes

sample

sensor


quadrant(812=96 pixels)96-channel

front-end(3 32 channel ASICs)

Peltier

20mm

398-element silicon pad array for absorption spectroscopy and/or x-ray microprobes.

Central hole for incident pump beam to allow close approach to sample.

Uses 12 ASICS. Peltier cooled to -

35 deg. C.

High-rate multi-element detector for fluorescence measurements


55Fe spectrum

50µm-gap, Cp 700fF, Ci-bond 50-200fF, Ci-pad 220fF

0 1 2 3 4 5 6 7 81

10

100

1k

10k

FWHM : 184eV, electronics : 147eV (17e-)

Energy Resolution - single channel

Fe55

T = -26C

Rate = 250Hz

Pixel gap = 50µm

Peaking Time = 4µs

C

ou

nts

Energy [keV]


ASIC control and readout ASIC functions controlled by high-speed synchronous

serial bit stream (SPI). 904 bits / chip, 4MHz

Data read out in same manner. 2304 bits / chip.

Threshold levels controlled by global DC levels (DACs). 32 x 4 offset trim DACs (6-bit) on-chip.

External counter gate signal. Counter contents cleared on readout

No read-while-counting.


Token-passing serial interface Chip is selected by Tin high.

All SPI I/O operates on selected chip.

Toggling Tclk passes token through to Tout, and Tin is taken low.

Tout is passed to Tin of next chip, causing it to be selected.

Next Tclk passes token to next chip, and passes low level to the one just read.


Embedded EPICS IOC

READOUT


EPICS and RTEMS

EPICS http://www.aps.anl.gov/epics Powerful, widely used, open-source control system, based

on an active database Distributed client-server architecture Many convenient features.

RTEMS http://www.rtems.com/ Open-source real-time operating system

similar functionality to VxWorks No license hassles Active development community


Embedded IOC

EPICS/RTEMS IOC embedded in microprocessor system. Motorola Coldfire MCF5272 processor 4Mb flash ROM, 8Mb DRAM On-chip 100Mb ethernet, serial, SPI, bit I/O Low-cost credit-card format system (Arcturus Neworks

uCdimm 5272) Daughter board holds 16 12-bit DAC channels, 8 12-bit ADC

channels, peak-detect/hold, detector bias supply, Peltier current regulator.


EPICS database for detector Custom EPICS record, similar to standard scaler record, but with

additional arrays to control all of the ASIC functions. Auto-count facility Retrieve all scaler contents or sum all channels Threshold trim DAC control Gain & Shaping Time control individual channel disable & test pulse enable analog pulse output select

Standard EPICS analog out and in records control global window thresholds and read various values.

Makes integration with beamline much easier. Can use wide range of tools and languages to implement user

interfaces (C,Python,Matlab,Labview)


MEDM user interface Standard EPICS facilities

allow quick GUI development, much easier than conventional GUI toolkits.

Device looks very similar to the standard EPICS scaler device, but with many more channels and additional detector control functionality.

Thresholds set via on-board DACs accessed as 'ao' records.


Automatic threshold equalization

before correction 170e- rms

after correction 2.5e- rms


400 channels, < 300 eV, > 10MHz

New EXAFS detector


Drift-Detector Array

Drift-detectors give large area while keeping low capacitance by ‘drifting’ charge through bulk of silicon to a small collector electrode.

Wafer has 96- and 384-element arrays.


Non-spectroscopic applications

Strip-shaped pixels form a 1-D position sensing detector with energy resolution (~350eV).

320 strips on 0.125mm pitch -> 40mm total length

Strips 8mm long Useful for diffraction

and scattering experiments.


Powder diffraction

Detector length = 40mm Sample-detector

distance = 263mm -> 8.7 degrees

coverage, 0.03 degrees / strip.

13 measurements spaced 7.5 degrees apart, each 1 second count time.

Total 20 sec. scan.


Next step

Work towards a system providing full spectrum per channel, instead of hardware windows

Same low-noise analog front-end Integrate BNL Peak-detect / derandomizer module,

modified for time-over-threshold mode. Fast ADC + FPGA + CPU to process data

Try to replace pad detectors with drift detectors.


Summary

We have developed an ASIC for low-noise photon-counting applications, and combined it with low-leakage silicon diode-based detector elements; square pads for spectroscopy and strips for diffraction.

We have developed an interface based on a System-on-chip microprocessor, using EPICS and RTEMS.

We are applying these detectors to problems in X-ray spectroscopy, scattering and diffraction

They provide low noise (good energy resolution) and high count rate. Planning a next-generation chip for microprobe applications.

brookhaven science associates u.s. department of energy multi-element silicon detectors for x-ray...

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