Transcript Poster - Indico

Analysis of CMOS APD with Geiger mode
1,2Leem
Hyun Tae,1,2Kwang Hyun Kim*, and 3Chung Young Hyun
1Biomedical Engineering, Jungwon University, Republic of Korea
2Basic Atomic Energy Research Institute (BAERI), Jungwon University, Republic of Korea
3Department of Radiological Science, College of Health Science, Yonsei University, Wonju, 220710, Republic of Korea
E-mail: [email protected]
I. Introduction
Dead Time
High performance radiation sensors, which are used in nuclear medicine
equipment such as the Positron Emission Tomography(PET) should be
sensitive to a low amount of light and it should be able to get information
from a photon. The Photomultiplier tube(PMT) can satisfy the conditions of
a High performance radiation sensor. However, the high voltage
consumption and the large volume are disadvantages of the PMT.
The existing SiAPD and SiPM cannot realize a circuit which can process
electrical signals on the same chip. However, the 0.35μm Complementary
Metal Oxide Semiconductor(CMOS) process is able to integrate with signal
processing circuits in one chip. Because the performance of the SPADs
governs the characteristics of the SiPM, many researchers have
investigated the SPADs manufactured in different CMOS processes.
Our purpose for this research is the optimization of the Fill Factor
size(17.4%, 23%) of the P+/N structure Geiger mode silicon APD base of a
standard Complement Metal Oxide Semiconductor(CMOS) 0.35μm
technology of two poly-four metal process. We produced results of the dark
current, photo current, gain, dead time, and dark count rate in order to
evaluate characteristics and performances of silicon APD.
The photon count rate of the CMOS APD is limited by dead time.
Therefore, dead time decides the sensitivity of the CMOS APD according
to each fill factor.
The quenching resistance was
200kΩ and the load resistance was
50Ω. The overvoltage was
increased by 1V steps from 19V to
23V.
Fig.5. The quenching circuit for the Dead Time
0.05
0.05
0.00
0.00
19V
20V
21V
22V
23V
Voltage(V)
-0.10
-0.15
-0.20
-0.25
-0.10
-0.15
-0.20
-0.25
-0.30
-0.30
-0.35
II. Materials and Methods
19V
20V
21V
22V
23V
-0.05
Voltage(V)
-0.05
Fill Factor: 17.4%
-0.40
-40
-20
0
20
40
60
Fill Factor: 23%
-0.35
-40
80
-20
0
20
60
80
Time(nsec)
Time(nsec)
We used the P+/N structure Geiger mode silicon APD base of a standard
Complement Metal Oxide Semiconductor(CMOS) 0.35μm technology of
two poly-four metal process and compared the fill factor of 17.4% and the
fill factor of 23% at Fig.1 and Fig.2
40
Fig. 6. Dead Time of CMOS APD
It is determined that 80% of a pulse’s time division is dead time. The dead
time of a fill factor of 23% is 21nsec, and the dead time of a fill factor of
17.4% is 20nsec.
Gain
Gain
3.0x10
6
2.5x10
6
2.0x10
6
1.5x10
6
1.0x10
6
5.0x10
5
As a result of this experiment, when the
overvoltage was increased, it was shown
that a fill factor of 23% will get a higher
gain than a fill factor of 17.4% at
1.28E+05.
Fill Factor 17.4%
Fill Factor 23%
0.0
Fig. 7. Gain VS Overvoltage
Fig. 1. Two geometries manufactured in 0.35 um CMOS process.
19
20
21
22
23
Overvoltage(V)
Dark Count Rate
Fig. 2. Two P+/N structure CMOS APDs considered in this study.
The definition of the dark count rate is that the number of dark current
which occurs by thermal electrons per second and it can be expressed as
threshold and overvoltage.
Therefore, the dark count rate is a pointer to express the noise of the
CMOS APD when it is operating in Geiger mode.
4
Dark Current and Photo Current
 The dark current experiment and photo current experiment were used to
estimate the I-V characteristics of this photodiode.
When the dark current and photo current were measured, we blocked out
all light and the temperature of the lab was 23°C. The dark current and
photo current were measured as a function of reverse bias with 0.1V steps
up to 20V.
1E-3
Fill Factor 23%
Fill Factor 17.4%
1E-4
3
10
10
2
10
19V
20V
21V
22V
23V
3
10
2
10
Fill Factor: 23%
Fill Factor: 17.4%
0
100
200
300
400
500
600
threshold(mV)
700
800
900
1000
0
100
200
300
400
500
600
700
800
900
1000
Threshold(mV)
Fig.8. Dark Count Rate
The level of a single photoelectron on a fill factor of 17.4% was about
9.8kHz, and on a fill factor of 23% it was 14kHz.
1E-4
1E-5
IV. Conclusion
1E-5
1E-6
Current(A)
Dark Current(A)
FF 23%
FF 17%
1E-3
4
19V
20V
21V
22V
23V
Dark Count Rate(Hz)
III. Result and Analysis
Dark Count Rate(Hz)
10
1E-7
1E-8
1E-6
1E-7
1E-8
1E-9
1E-9
1E-10
1E-10
1E-11
1E-11
0
5
10
15
20
Reverce Voltage(V)
Fig.3. Dark Current
I-V characteristics
0
5
10
15
20
Reverce bias(V)
Fig.4. Photo Current
I-V characteristics
 Break downs of all the CMOS APD occurred at 19.1V. At this voltage, the
electron event in the active area produced a very large current flow with
amplification gain of up to 106 ~108.
The I-V characteristics of the dark current and photo current showed
both the linear mode and Geiger mode by break down voltage.
On reverse bias 20V, the fill factor of 23% produced both a dark and
photo current of 1.7mA more than the fill factor of 17.4%.
 We compared fill factors of 23% and 17.4%. The break down voltage of
each fill factor was near 19V though both the dark current and photo
current. Fill factor 23% flows more current than 17.4% at same reverse
voltage.
This research also proved that the size of fill factor was the proportion to
the gain.
However, when we checked the fill factor of 23% it had a decreased
sensitivity of 1nsec more than the fill factor of 17.4%. The result of the
dark count rate verified that the fill factor of 23% created more noise than
a fill factor of 17.3%.
Therefore, we should consider efficiency according to the dark count rate,
dead time, and gain and determine the optimization of the CMOS APD.
In the near future, we will design the 0.35μm CMOS APD 2 dimensional
array base of this research for radiation imaging.