SiPM
Photon counting device consisting in APD pixels operating in Geiger mode.
Each pixel outputs a signal when it detects one photon.
The signal output is the total sum of the outputs from all the pixels.
Pixel dimensions can range from 15x15 m2 to 100x100 m2 ore more
Applied voltage higher
than breakdown voltage
p on n
n on p
Geiger mode
overvoltage= supplied voltagebreakdown voltage
High gain (105-107), good time resolution, insensitive to magnetic field, small size,
small operating voltage (below 100 V), high integration level
Critical issues: dynamic range, noise (dark current), optical cross-talk ,
response stability vs. voltage and vs. temperature
The assembly can be monolithic (a single silicon die with several SiPMs)
or hybrid ( several silicon dies on a common package)
Hamamatsu monolithic array S11828-3344M
4x4 channels. Each channel has a photosensitive area of 3x3 mm2,
made of 3600 pixels with a 50m pitch
Distance from photosensitive area to edge of mount package surface:
500m
Single photons produce a signal of several millivolts (on a 50 ohm load)
Output: A=Ai (as long as the number
of photons in a pulse in much smaller than
the number of cells)
Two ore more photons in the same cell at the
same time give the same signal as one photon
When Nph > 50% of cells, the deviation from
linearity is more than 20%
Gain variation vs. voltage and temperature
Hamamatsu
AdvanSiD
For stable
operation, if the
AdvanSiD
temperature is
recently quoted:
25 mV/0C breakdown not fixed, one
has to correct
voltage variation
the voltage to
compensate
(feed-back
needed)
PDE (photon detection efficiency)
PDE=QE ·  · Ptrigger
geometric fill factor
decreases with the number of cells
Dynamic range increases with the number of cells
 is improving with progress of technology.
from AdvanSiD: 70% for 30 m cells
p on n (Hamamatsu)
n on p (Photonique)
Dark current
Dark counts can be triggered by free carriers generated even in the absence
of an incoming photon. Dark current increases with overvoltage and temperature.
At 25 0C it can reach a rate from 100 kHz to several MHz per mm2
It can be reduced by putting a threshold on the number of photons
(almost one order of magnitude per 1 photoelectron amplitude of threshold)
AdvanSiD 1x1 mm2, 50m cells
Optical crosstalk
It happens when a photon of an avalanche travels to a neighboring cell.
More critical in the range 850-1100 nm. Can be of the order of 5-7% (gain dependent)
Greatly improved using “groove” technique for cell separation (less than 1%)
Pulse shape
Rise time determined by silicon and neutral region resitance, space charge, capacitance
of the whole device (dominated by the parasitic capacitance of the line connecting
the cells to the bias voltage)
C: about 10 pF; trise : some nanoseconds
Timing
from FBK (commercial branch: AdvanSiD)
1x8 SiPM Array - monolithic
1.5x1.5 mm2 SiPM
Backside: pads for the 8
independent channels
• Monolithic
– Silicon die with 8 1.5x1.5 mm2 SiPMs
– 1.7 mm SiPM pitch
– 200um gap between SiPMs
1x8 SiPM Array - Hybrid
• Hybrid array
–
–
–
–
8 Silicon dies on common package
1.2 mm circular SiPMs
1.7 mm SiPM pitch
Lower fill factor w.r.t. monolithic array
• CSP SMD package
– 8 channels
– 260um epoxy resin coating (etched in between SiPMs)
31 July 2017
Company Confidential
Another hybrid