Upload
others
View
1
Download
0
Embed Size (px)
Citation preview
Bruce GnadeUT Dallas
Thin-Film Semiconductor Technology Applied to Large Area Radiation Detectors
CIRMS Conference 2012October 23, 2012
Flexible Electronics Research Group at UTD
• POST‐DOCS/STAFF SCIENTISTS– Dr. I. Mejia, Dr. Kurtis Cantley, Dr. M. Jia, Dr. I. Trachtenberg, Dr. A. Carrillo, Dr. N.
Hernandez, Dr. J. Conde, Dr. Dick Chapman • GRADUATE STUDENTS/PROJECTS
– Ana Salas– PhD. – Alternate Contacts (AFOSR)– Duo Mao – Ph.D. – Organic Memory (ARL)– Mike Perez, Ph.D. – n‐type flexible TFTs (NSF)– John Murphy Ph.D – Large Area Neutron Detectors (ARL, FUSION)– Martha Rivas – Pulsed Laser Deposition of Chalcogenides– Dewan Lutful Kabir – Reliability and Electrical Characterization– Lindsey Smith – Neutron converter layers (DNDO)– Kevin Larosa – Backplane electronics (DNDO)
• VISITING SCHOLARS– J. Ramos (UACJ), V. Martinez, (CIMAV), G. Gutierrez (CIMAV), Alfredo Luque (CNyN)
• Collaborators– Dr. David Allee (ASU), Dr. Eric Forsythe (ARL), George Kunnen (ASU)
• FUNDING– U.S. Army Research Labs,Military Tech, DOE, UT Dallas, Texas MicroPower, NSF, Texas
instruments, FUSION, DNDO, AFOSR, DARPA
Agenda
• Large Area Radiation Detectors– Why thin‐film devices– Large area neutron detector project
• Current state of thin‐film semiconductor devices– Transistors– Memory– CMOS– Circuits
Why large area detectors?
Neutron Source
08 ft 8 ft
2” 3He tube
Large area neutron detector
Probability of neutron hitting 2” tube ~ 1 part in 36000Probability of neutron hitting large area detector ~ 1 part in 3
# of TFTs per min
Area per min
Yield zero redundancies
Display ~cost/cm2
Si-CMOS($5k/wafer)
Digital X-ray 1-up/subs
Digital x-ray4-up/subs
~108/min 4m2/min 99.99997% $0.05/cm2 $6.86/cm2 $29/cm2 $7/cm2
Displays
Source: Organic and Printed Electronics, Organic Electronics Association (OE‐A) Broucher,
3rd Edition, 2009
Throughp
ut (m
2 /sec)
Minimum feature Size (m)
10‐4
1
100
1 100 50010
Digital X‐ray imagers
Future Flexible Electronics Throughput vs cost/cm2
Thanks to Dr. Eric Forsythe – Army Research Laboratory
Large Area Sensor Arrays: The Concept with ASU
RESET
AMPLIFIER
READ
ROW
PIXEL
Energy to charge conversion
•Neutron Detection•VIS / IR Imager• Millimeter Wave• MEMs
• Blast• Acoustic
• Electronic Textiles
Very large area, flexible, low power neutron detectors
Three main pieces‐ energy conversion layer‐ sensing diode‐ backplane electronics
Sensing diode
Flexible substrate (~1 mm)
Al (100 nm)
Au (100nm)
6Li 10B nanoparticle composite
Au (100 nm)
Sensing diode
Flexible substrate (~1 mm)
6Li nanoparticles 10B
Al (100 nm)
Isotope ReactionThermal σ(barns)
Charged particles and energies (keV)
3He 3He(n,p)3H 5333 p: 573, 3H: 1916Li 6Li(n,α)3H 940 3H: 2727, α: 205510B 10B(n,α)7Li 3835 α: 1472, 7Li: 480natGd natGd(n,γ) 49700 Conversion e‐: 29‐191157Gd 157Gd(n,γ) 259000 Conversion e‐: 29‐182235U 235U(n,f) 681 Various fission products
Neutron conversion layer strategies
Converter‐on‐diode Converter‐in‐diode
Neutron Detector Modeling in MCNPX and MATLAB
• Front end captures Neutron and emits charged alpha particle,• Alpha detected with PIN diode and active pixel sensor circuit• MCNPX used to model and optimize detector front‐end layers• Detector layers capable of being fabricated with FDC process
With Correlated DoubleSampling applied:
Detector Layers simulated in MCNPX:
Weapons Grade Plutonium
MATLAB model of arrayed pixel sensors with simulated alpha particle exposure (Red Boxes):
Example neutron conversion layeroptimizations result in 2.6um 10B thickness
• Each cell represents an active pixel sensor• Sensors modeled to reflect FDC process variations.• CDS dramatically improves ability for detector to resolve alpha particle strikes
Thin‐film diode optimization ‐MCNPX
TABLE II. Intrinsic gamma efficiencies for selected thicknesses and gammaenergies. (LLD = 300keV and a 2.8 µm 10B conversion layer)
Thickness(μm)
γ energy (keV) Si CdTe GaAs ZnO
3 5111460
00
09×10-14
00
08×10-14
10 5111460
01×10-13
6×10-13
9×10-1202×10-12
1×10-12
8×10-12
30 5111460
6×10-11
1×10-106×10-7
2×10-71×10-7
6×10-83×10-7
2×10-7
100 5111460
3×10-6
2×10-64×10-4
1×10-42×10-4
6×10-52×10-4
9×10-5
300 5111460
3×10-4
2×10-44×10-3
3×10-32×10-3
2×10-32×10-3
2×10-3
Sensing Diode Optimization: Schottky vs. MIS
Detector bias (V) 0V 5V 20V
Particles detected 562 595 651
Measured source strength 1,938 1,954 2,245
Efficiency 60% 60% 69%
Integrating over channels for peak
Integrating over channels 100‐450
Detector bias (V)
0V 5V 20V 100V
Particles detected 785 772 752 869
Measured source strength
2,486 2,445 2,382 2,752
Efficiency 77% 76% 74% 85%
Radiation measurement setupPreamp
Amp and det bias
Oscilloscope
Sample chamberMCA
TFT‐based Active Pixel Sensors
The detection of two alpha particle strikes on a commercial diode and amplified with the two stage low noise thin film transistor amplifier.
NMOS
VGS (Volts)
-30-20-10010
log(
| ID
S |)
( A
)
10-4
10-3
10-2
10-1
100
101
102
Sqrt
(ID
S) (
A)1/
20
1x10-3
2x10-3
3x10-3
4x10-3
5x10-3
W/L = 400m/7mVDS = -25V
VDS (Volts)
-30-25-20-15-10-50
I DS
(
0
2
4
6
8
10
12W/L = 400m/7m VGS = -20V
VGS = -15V
VGS = -10V
VGS = -5Vcc
Flexible CMOS
Why CMOS– Dramatically reduced power consumption
– Analog circuitry possible
–Sensor applications
How to do F‐CMOS–Combine Processes
• N‐Type a‐Si:H TFTs• N‐Type inorganic TFTs• P‐Type Organic TFTs
–Standard Cell Approach
PMOS
a‐Si / pentacene CMOS Devices – with ASU
VIN (V)0 5 10 15 20
V OU
T(V)
0
5
10
15
20
Gai
n
0
4
8
12
16
Vin Vout
pmos
nmos
VDD
GND
Inpu
t (V)
0
5
10
15
20
25
Time (seconds)
-0.02 -0.01 0.00 0.01 0.02
NA
ND
Gat
e O
utpu
t (V)
0
5
10
15
20
25
A
B
Inpu
t (V)
0
5
10
15
20
25
Time (seconds)
-0.02 -0.01 0.00 0.01 0.02N
OR
Gat
e O
utpu
t (V)
0
5
10
15
20
25
A
B
Inverters NAND Gates NOR Gates
Inorganic semiconductors: 100 cm2 V-1 s-1
Amorphous silicon: ~ 0.01 to 1 cm2 V-1 s-1
Organic semiconductors ~ 6x10−2 to 1 cm2V-1 s-1
Technology Comparison
SemiconductorMobility (cm2/V‐s)e‐ h+
CdS 250
CdSe 650
ZnSe 600
SnSe2 27
InS 50
SnS2 18
CuGaS2 20
CuInS2 15
ZnTe 100
PbS 5
Cu2S 10
Chalcogenides
ZnO
CdSCdTe
ZnS
ZnSe
CdSeZn
TeCuInSe2
CuInS2CuInTe2CuAlSe2CuGaS
e2
Elec
tron
or H
ole
Con
cent
ratio
n (c
m-3
)1014
1015
1016
1017
1018
1019
1020
1021
1022
P
PP
P
PP
P
PP
P
P
P
N N
N NN N
N N
N
N N N
N-TYPE P-TYPE
CBD CdS/ Evaporated Pentacene Inverters
• Optimized pentacene and CBD CdS deposition
• Inverters yield gains of about 80
VI
N
VOUT
0 5 10 15 20
0
5
10
15
20
GAIN
VIN [V ]
VOUT [V
]
VOUT
0
20
40
60
80
100
G A IN
Ferroelectric‐based organic Memory (FeRAM)PVDF ‐ TrFe
C
F F
H
C
H
C
F F
H
C
H
P
MFM Capacitor – 1T‐1C memory cell‐ relatively easy to fabricate‐ destructive read‐ complicated read / write circuitry
Au
Ferro‐electric
Gate – Au
Fully integrated TFT used for 1T1C
0 2 4 6 8 10 12 140.0
20.0µ
40.0µ
60.0µ
80.0µ
100.0µ
120.0µ
I D [A
]
VD [V]
VG = 0 V VG = 2.5 V VG = 5 V VG = 7.5 V VG = 10 V VG = 12.5 V VG = 15 V
W = 160 umL = 5 um
-5 0 5 10 15
0.000
0.002
0.004
0.006
0.008
0.010
0.012
0.014
0.016
W = 160 umL = 5 um
SQ
RT
I D [A
1/2 ]
VG [V]
SQRT ID
FET = 1.5 cm2/V-sVT = 5.5 V
VD = 15 VSaturation
1E-12
1E-11
1E-10
1E-9
1E-8
1E-7
1E-6
1E-5
1E-4
1E-3
ABS ID
ID [A]
1. CBD CdS as the semiconductor2. ALD HfO2 as the gate dielectric3. Parylene as ILD4. Low temperature process,
maximum temperature is 100 oC
2T2C FRAM Characterization
DWLWEDWL
CL0
GND
WL0
SL
SRGND
PLCL1
CL2CL3
CL4CL5
CL6CL7
WL1WL2
WL3WL4
WL5WL6WL7
BAL
64‐bit FRAM layout
20
• The output signal from the sensor element is a low voltage pulse with 10’s ns width, with very high impedance due to the capacitive nature of the device.
• Charge amplifiers provide very high input impedance ‐ they integrate weak charge pulses to convert them into voltage pulses with low impedance.
[1] F. J. Ramirez‐Jimenez et al., Nuclear Instruments and Methods in Physics Research A, 497, (2003), 577‐583.[2] Bernd J. Pichler et al., IEEE Transactions on Nuclear Science, 48(6), (2001), 2370‐2374.[3] HAMAMATSU, model H4083.
In‐pixel charge amplifier – Ramirez designPrototype neutron detector
Potential Advantages
• Very large aperture at moderate cost based on AMLCD • In‐pixel electronics provide low capacitance for pixelated array• Potential for high γ‐ray rejection rate due to TFT array electronics• Potential for fission neutron multiplicity measurements • Potential for determination of directionality of the neutron source
Thank You!