Vertex05, 8/11/05 Jaap Velthuis, Bonn University
DEPFET Status• DEPFET Principle• Readout modes• Projects:
– XEUS– WIMS– ILC
• ILC Testbeam results• Summary & Outlook
Univ. of Bonn: M.Karagounis, R.Kohrs, H.Krüger, M. Mathes, L.Reuen, C.Sandow, E.von Törne, M.Trimpl, J.Velthuis, N.Wermes
Univ. of Mannheim: P.Fischer, F.Giesen, I.Peric
Politecnico di Milano:M. Porro
MPI Halbleiterlabor Munich:O Hälker, S. Herrmann, L.Andricek, G.Lutz, H.G. Moser, R.H.Richter, M.Schnecke, L.Strüder, J.Treis, P.Lechner, S. Wölfel
THCA of Tsinghua Univ.:C. Zhang, S.N. Zhang
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
DEPFET Principle
• A p-FET transistor is integrated in every pixel.• By sidewards depletion potential minimum created below
internal gate.• Electrons, collected at internal gate, modulate transistor current
~1µm
p+
p+ n+
rear contact
drain bulksource
p
sym
met
ry a
xis
n+
ninternal gate
top gate clear
n -
n+p+
--
++
++
- 50
µm
------
MIP
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
DEPFET Principle
• Advantages:– Fast signal collection due to fully depleted bulk– Low noise due to small capacitance and amplification in
pixel– Transistor can be switched off by external gate – charge
collection is then still active !– Non-destructive readout
• Disadvantages:– Need to clear internal gate. This still requires high
voltages.
• 2 readout modes:– Source follower mode readout. Signal is voltage (XEUS)– Drain readout. Signal is current (WIMS&ILC)
required
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
SOURCE FOLLOWER
• Constant bias current IBias provided• Charge at internal gate translates into source voltage node change• Speed depends on overall load capacitance• Slow (t≈CL/gm≈3µs), but excellent noise
Clear
Clear-gate
Drain Source
GateDEPMOSdevice
Ibias
Buffer /amplifierIbias
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
DRAIN readout
• Measure Idrain directly• Fast response: limited by RC time of input resistance CURO and
Cload (~ns)
Clear
Clear-gate
Source Drain
GateDEPMOSdevice
Vout
CURO: currentamplifier
transimpedenceamplifier
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
DEPFET Applications
• DEPFET under study for:– XEUS
• Exploring the early universe by imaging spectroscopy in the X-ray band
• Need noise < 4e-
• Source follower mode
– WIMS• Wide-band Imaging and Multi-band Spectrometer, part of
China’s spacelab mission• Drain readout
– ILC• Need row rates of 20MHz• Drain readout
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
XEUS
• Exploring the early universe by imaging spectroscopy in the X-ray band
• Detector:– Device active area 7.68 x 7.68
cm2
– Monolithic sensor integrated onto a single 6“ wafer
– Device thickness 450 µm– Pixel size 75 x 75 µm2
– Position resolution ca. 30 µm– Total 1024 x 1024 pixel cells– Total readout time / frame
1.25 ms– Processing time per detector
row 2.5 µs
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Excellent noise
• Single pixel device • 10 µs shaping• Room
temperature (22° C)
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Excellent noise
• Large structure (64x64):– 75 x 75 µm2 pixel size – 45 µm gate circumference
/ 5 µm gate length– Drain in center of pixel– Cut gate geometry– Curved edge– Double metal
• Operated at:– Pixel current 30 µA– Line processing time 25 µs
0 1 2 3 4 5 6 71
10
100
1000
10000
Si-KAl-K
Mn-KMn-K
Cou
nts
Energy (keV)
Escape Peak
Energy resolution: 126 eV FWHM @ Mn-Ka Line
corresponding to 4.9 e- ENC
-60 -40 -20 0 20
10
20
30
40
50
60
70
2.78
5.56
8.33
11.11
13.89
16.67
19.44
Normal cycles (tInt
= 3 ms)
Reference cycles (tInt
= 5 s)
Pix
el r
ea
do
ut n
ois
e (
e-
EN
C)
Pix
el r
ea
do
ut n
ois
e (
eV
)
Temperature (°C)
Noise dependence
Pixel readout noise: 63 – 14eV (17 – 3.6 e- ENC)
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
WIMS
• Wide-band Imaging and Multi-band Spectrometer (WIMS) is part of China’s spacelab mission .
• Observe high-energy bursts, transients and fast-varying sources over a broad spectral range simultaneously
• Using Macro pixels– Pixel size 0.5x0.5 mm2
– “Si-drift chamber readout using DEPFET”
0 1000 2000 3000 4000 5000 6000 70000
100
200
300
400
500
600
700
800
FWHM = 209 eV
ENC = 19.1 el r.m.s
Room temperatureBack side illuminates, fast drain readoutShaping time: 3μsClear pulse period 1 ms with width 3 μs
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
DEPFET for ILC
• Basic system • Clearing• ILC requirements• Ladder proposal• Power consumption• Thinning• Radiation hardness• Testbeam results
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Basic system
• Select and Clear signals provided by SWITCHER – 64 x 2 outputs– Max ΔV = 25V
• Read out row-wise: CURO– current based read out– 128 channels– CDS – real time hit finding
& zero-suppression– row rate up to 24 MHz
n x mpixel
IDRAIN
DEPFET- matrix
VGATE, OFF
off
off
on
off
VGATE, ON
gate
drain VCLEAR, OFF
off
off
reset
off
VCLEAR, ON
reset
output
0 suppression
VCLEAR-Control
Gate Switche
r
ClearSwitche
r
Current Readout CUROII
DEPFET Matrix64x128 pixels, 36 x
28.5µm2
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
HighE vs non-HighE
• HighE extra n-type implant– Moves internal gate
deeper into bulk– Clearing takes places
deeper in the bulk– Lower signals, but
easier clearing
clear
Internal gate
channel
Optional HighE implant
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Clearing
• CURO measures: Isig,i+Iped,i & Iped,i+1
• Need to remove all charge such that Iped,i+1=Iped,i
• COMPLETE CLEAR possible for HighE with low voltages (~7V)⇒ possible to make radhard SWITCHER in standard CMOS
HighE
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
ILC requirements
• Time structure: 1 train of 2820 crossings in ~1 ms every ~200ms– Hit density: for r = 15 mm: ~ 100 tracks / mm2 / train– Row readout rate: > 20 MHz – Occupany < 0.5 %
• Radiation length: ~0.1% X0 per layer– thinned sensors (50 μm) – low power consumption
• Radiation tolerance: 200 krad (for 5 years operation)
• Resolution: few µm ( pixel size ≤ 25 x 25 µm2)
950 µs 199 ms 950 µs
2820 bunches
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Ladder proposal
• Modules have active area ~13 x 100 mm2
• Read out on both sides.
• Detectors 50µm thick, with 300µm thick frame yields 0.11% X0
• SWITCHER & CURO chips connected by bump bonding
SWITCHER
CURO
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
ILC Power
• Measured Power Dissipation:– Switcher: 6.3 mW per active channel at 50MHz– CURO: 2.8 mW / channel
• Assumed Power Dissipation of DEPFET Sensor:– 0.5 mW per active pixel– duty cycle: 1/200
• Only active pixel dissipate power– 1024 active pixels per module– 8 modules in Layer 1 => 8192 active pixels
• Expected Power Dissipation in Layer 1– Sensor: 8192 x 0.5 mW / 200 = 20 mW– Switcher: 16 x 6.3 mW / 200 = 0.5 mW– Curo: 8192 x 2.8 mW / 200 = 114 mW
• For Layer 1 Sum: 135 mW
For 5 Layer DEPFET Vertex Detector: Total ~ 3.6 W no active cooling
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Thinning
sensor wafer
handle wafer
1. implant backside on sensor wafer
2. bond wafers with SiO2 in between
3. thin sensor side to desired thick.
4. process DEPFETs on top side
5. etch backside up to oxide/implant
first ‘dummy’ samples:50µm silicon with 350µm frame
thinned diode structures:leakage current: <1nA /cm2
Thinning technology for active area established
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Radiation hardness
• Irradiations with 60Co and X-rays (~17keV) up to ~1Mrad (SiO2)
• Threshold shift of the MOSFET (~4V) can be compensated by bias voltage shift
60Co
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Testbeam
• DESY test beam with 6 GeV e- • Bonn ATLAS telescope system:
– double sided strip detectors– pitch 50 µm (no intermediate strips)– readout rate 4.5 kHz (telescope only)
• DEPFET:– 128x64 (28.5x36 µm2)– 450 µm thick– Frame time 1.8 ms
DEPFET
beam
1 2 3 4Scintillator Scintillator3 x 3 mm²
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Pedestal & Noise
• Pedestal: average signal after hit removal• Noise: standard deviation after pedestal,
common mode and hit removal
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Clustering
• Look for clusters:– Seed
• pixel largest signal • seed cut >5σ
– Neighbours• Neighbour cut >2σ
• Combine signals seed & neighbors
• S/N3x3=125.9±0.2– Noise higher than
expected– Next generation expect to
reduce noise by factor 2
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Position resolution
• Hit positions reconstructed using the CoG algorithm• Note: pixelsize X=36µm Y=28.5µm• Terrible, but … due to multiple scattering
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Multiple scattering
• Eelectron only 6GeV
• Telescope planes 10cm apart
• Minimize effect scattering by selecting hard tracks using 2 cut
• Price: lose statistics
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Multiple scattering (II)
• Performed simulation.• Using Fraction remaining
tracks, telescope uncertainty can be estimated.
• From CERN testbeam know that σintrinsic~5-6µm, but not compared S/Ntel
• σX=9.71±0.02µm, σY=9.31±0.02µmσ intrinsic X Y
5µm 5.9 5.2
6µm 3.9 2.7
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
HighE matrix
• HighE implant moves internal gate into bulk– Lower signal– Easier clearing
• Results:– S/N3x3=99.5±0.1
– σX=9.11±0.03µm, σY=8.80±0.03µm
– Somewhat larger clusters yield better position resolution
Poor stats& fit
σ intrinsic X Y
5µm 4.8 4.3
6µm 1.9 --
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Summary
• DEPFET integrates MOSFET in fully depleted bulk. Developed towards: – XEUS mission:
• Slow readout (source follower mode)• Excellent noise (~2.2e-)
– WIMS mission• Very large pixels (0.5x0.5mm2) • Si-drift chamber readout by DEPFET• Fast(er) readout (noise=19e-)
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Summary (II)
• Developed towards ILC. Meets already demands on– Radiation length (0.11 X0)
– Radiation hardness (ΔVth shift~4V@1Mrad)– Power consumption (<5W full detector)– Position resolution (≲5µm)
• Excellent S/N:– S/N=126 without HighE– S/N=100 with HighE– ⇒can thin detector to 50µm with still good S/N
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Outlook
• Improving the system to increase readout speed.– Individual parts already function well at ILC
speed
• Testbeam at DESY (6GeV electrons) with better mechanics and at CERN. Goals:– Improve S/N– Test zero suppression
• Build 512x512 matrix
Vertex05, 8/11/05 Jaap Velthuis, Bonn University
Author list
Univ. of Bonn: M.Karagounis, R.Kohrs, H.Krüger, M. Mathes, L.Reuen, C.Sandow, E.von Törne, M.Trimpl,
J.Velthuis, N.Wermes
Univ. of Mannheim: P.Fischer, F.Giesen, I.Peric
Politecnico di Milano:M. Porro
MPI Halbleiterlabor Munich:O Hälker, S. Herrmann, L.Andricek, G.Lutz, H.G. Moser, R.H.Richter, M.Schnecke, L.Strüder,
J.Treis, P.Lechner, S. Wölfel
THCA of Tsinghua Univ.:C. Zhang, S.N. Zhang