FAQ2018-04-19T07:07:31+00:00

FAQ

The SiPM is designed to operate in Geiger mode, i.e. the applied bias voltage is higher than the breakdown voltage and the cathode is positively biased with respect to the anode.

Please refer to the Biasing and Readout tech note.

Amplification is generally required for detection of low optical power levels.

Please refer to the Biasing and Readout tech note.

Provided operation is well above the breakdown (>2 V overvoltage) there is not a significant impact on the responsivity of the SiPM, given a typical ripple of a few mV. The change in voltage will affect the applied bias across the SiPM, resulting in a ripple in the responsivity, directly proportional to the change in overvoltage. 2  mV out of 2 V is a small effect, for example.

When looking for very precise signal measurements, it is certainly advised to minimise power supply noise. Apart from affecting the signal as above, you could get coupling through the diode that affects the Fast output and could impact the small signal when taking low light level measurements.

Please refer to the Biasing and Readout tech note for more information on bias filtering.

SensL provides evaluation ‘break out’ boards for accessing the signals on array products, but does not make or sell full readout systems. Our partners, AiT and Vertilon make and sell readout systems that can be used with SensL Arrays.

Large arrays can pose a readout challenge due to the many channels of amplifcation and processing that are required. Therefore, methods of reducing the number of channels are sometimes employed to reduce the readout requirements. Many examples of this can be found in the literature and in SensL’s tech notes, Readout Methods for Arrays and Signal Driven Multiplexing.

The user manuals for the ArrayC and ArrayJ products provide information on the using of the break out boards (BOBs) that SensL provide.

SensL does not offer power supplies

In a laboratory environment a Keithley source-meter or similar bench top voltage source can be used.

Our partners Nuclear Instruments and AIT both offer power supply options.

Nuclear Instruments provide the NIPM12 and NIPM12-U which are temperature compensated power supplies that can be quickly configured either over USB using i2C commands, or their software from a custom interface board, or through the integrated USB connector on the NIPM12-U.

AiT Instruments provide the HV80A and HV80B high accuracy power supplies.

A maximum current level is provided for each sensor in the product datasheet (links to datasheets can be found on the relevant product page.).

These limits should be observed to prevent thermal overload. This is not the same as the maximum signal capability of the SiPM.

SiPM photocurrent is self-limiting. The typical current consumption depends on the operating voltage and the light power incident on the SiPM. The expected output current may be estimated using the responsivity curve given in the datasheet. The X-axis is the wavelength of light in nanometers, while the Y-axis is the average  photocurrent per optical power, given in Amps per Watt.

The range of detectable powers is limited by the dynamic range of the SiPM. At high light power levels the SiPM will saturate, as all microcells fire continuously and the response will cease to be proportional to the incident light power.

There are a number of checks that you can perform to verify the SiPM is operating correctly

  1. A can be carried out quickly and simply using a multimeter to establish that the SiPM diode structure has not been damaged:
    1. Disconnect the SiPM from its circuit and using a multimeter in diode mode connect anode to positive lead and cathode to negative lead so the SiPM is forward biased. This should yield a 0.7 V drop across the diode
    2. Reversing the leads should present Hi or open circuit, provided all the microcells in the SiPM are intact.
  1. Check if the SiPM is responsive to light:
    1. Apply a suitable bias voltage across the SiPM and probe the standard output
    2. Cover the SiPM to prevent any light reaching the sensor. The standard output should produce 0 signal
    3. Allow some light to reach the sensor. The standard output should respond by increasing in amplitude. As the light power on the SiPM increases the standard output will approach saturation.
  1. An IV check can be performed, where the dark current is measured at several operating points. This may identify more subtle issue such as high leakage current
    1. Place the SiPM in a dark box or cover well with opaque material
    2. Apply a bias voltage to the SiPM that is below the breakdown voltage. Below the breakdown the dark current should be negligible, < 1 nA.
  • Apply a bias voltage that is a few volts above the breakdown voltage. The measured dark current should be close to the datasheet value specified for the SiPM.
  • A dark current that is significantly higher than the above result could be indicative of a short. If the SiPM is assembled on a PCB note that there could be additional leakage due to the PCB that should be accounted for

Notes: The above measurements (2 & 3) can be made by powering the SiPM with a Keithley source-meter or similar and measuring the SiPM signal with an oscilloscope.

The SiPM is extremely sensitive to light. To make a dark measurement a high quality dark box or opaque material should be used to block all ambient light.

For general advice, please refer to the Biasing and Readout tech note.

If building arrays of sensors on PCB, please refer to the Array Reference Design tech note.

Please see the Handling and Soldering guides for SMT/MLP sensors (for C-Series and R-Series sensors) or TSV sensors (J-Series).

The SiPM will not be damaged when exposed to high light power such as the lighting in a room or ambient outdoor light, provided the average current through the device does not exceed the maximum current rating in the datasheet.

SensL SiPMs are silicon sensors and therefore are capable of detecting wavelengths from 200 nm up to 1050 nm. The spectral response depends up.on the product family that is used. Please consult the product datasheet for the spectral range specification.

Light levels can be detected from picowatts up to microwatts using SiPMs. The dynamic range depends primarily on the number of microcells in the SiPM but can be further optimised to suit the application by changing the bias voltage.

When biased in Geiger mode, the SiPM produces a photocurrent proportional to the number of microcells that have fired, which provides a measure of the amount of light detected by the sensor.

The photocurrent flows through the sensor from cathode to anode and either of these terminals may be used as the standard output. Therefore the standard output provides current or charge information and can produce a signal whose amplitude is proportional to the incident photon rate.

The fast output is a capacitively coupled output that is derived from the fast switching pulse that occurs at the internal node of the microcell. Unlike the standard output there is no net charge transfer across the fast output. The fast output produces a high speed voltage pulse signal whose amplitude is proportional to the number of microcells that have simultaneously fired. The fast output provides information about the number of photons detected in a pulse but it does not provide DC information as from a continuous optical signal

The standard and fast outputs can be used in isolation or both can be read out simultaneously and either can be used for amplitude or high speed timing measurements. When not used the fast output should be left floating without any cables or wires attached.

Refer to the Readout and Biasing technical note for more information.

Attention: The internal data of table “39” is corrupted!

Both C-Series and J-Series SiPMs are blue sensitive sensors that have peak response at 420 nm.

C-Series sensors are available as 1 mm, 3 mm or 6 mm sensors, whereas the J-Series sensors are available in 3 mm, 4 mm and 6 mm sizes. They also differ in terms of package type and performance

C-Series products are assembled using a wire bond leadframe process encapsulated in a clear transfer molded package. The resulting MLP package is reliable, robust and suitable for SMT assembly in a wide variety of applications.

The C-Series sensors have the lowest noise.

J-Series products are created a Through Silicon Via (TSV) process where the terminal connections are made using a via through the silicon die to the solder balls on the back of the board. The package has  a glass cover on top of the sensor. The TSV package has minimal dead space around the active area of the sensor and so can achieve a higher fill factor when the sensors are formed into arrays.

The glass entrance window of the J-Series TSV package has better transmission of UV light and so J-Series sensors have sensitivity down to 200 nm, whereas the C-Series sensitivity cuts off around 300 nm.

J-Series products have higher microcell fill factor that results in a higher PDE and have optimised signal tracking layout for better timing performance.

SensL SiPMs are rated to -40 oC only. However, the following papers discuss the use and results of SensL SiPMs in cryogenic applications:

D. Whittington et al., “Scintillation Light from Cosmic-Ray Muons in Liquid Argon ”.

B. Rossi et al., “The GAP-TPC

Due to the fast rising edge on both fast and standard outputs, the signal can be affected by impedance mismatches in the circuit.

The SensL SMA evaluation board is intended to drive long cables and in this scenario impedance matching is necessary to avoid reflections and maintain good signal integrity, particularly with the fast output.

SensL uses the RFXF9503 balun to set up a 50 Ω impedance at the fast output of the SMA board for some SiPMs. This provides optimal fast output pulse amplitude and timing characteristics when used with a 50 Ω cable and 50 Ω scope termination. For 1mm devices the fast output capacitance is low enough to allow direct 50 Ω connection even through a long cable and so the balun is not required. Devices larger than 1 mm have higher capacitance and the balun optimizes the fast output performance in this case.

The standard output is terminated with an appropriate sense resistor to provide reasonably good signal performance for the standard pulse.

The balun is generally not required for application specific circuits as the signal is usually terminated at a short distance on the PCB.

SensL SiPMs cannot be used for direct detection of X-rays or beta radiation.  They can be used to indirectly detect X-rays or betas by coupling them to an appropriate scintillator.

SiPM sensors themselves are insensitive to magnetic fields because the charge carriers have very short path lengths due to the narrow depletion widths used. SensL SiPM sensors have been successfully operated in magnetic fields up to several T.

SensL J-Series TSV packaged sensors contain no ferrous metals and can be used in magnetic fields without interference.

SensL does not offer a reference design or Arduino specific product/shield. However, examples of interfacing to Arduinos to sensors can be easily found on the internet. Two examples of users who have interfaced SensL SiPMs with Arduinos are given below.

Valerio Bocci et al., “The ArduSiPM a Compact Transportable Software/Hardware Data Acquisition System for SiPM Detector”

Spencer N. Axani et al., “Cosmic Watch Desktop Muon Detector”

Care should be taken to ensure that the signal of interest can be sampled effectively by the ADC used. The rule of thumb is that the sampling frequency should be at least twice that of the signal frequency.

SiPM breakdown voltage, Vbr, increases with increasing temperature.

If the applied bias voltage is kept constant an increase in temperature will effectively reduce the applied overvoltage. This will result in lower gain and PDE. The temperature coefficient of breakdown is given in the datasheet for each sensor in mV/°C

To ensure stable PDE and gain in the presence of temperature fluctuations, either bias compensation or thermal regulation of the SiPM should be considered. With bias compensation a temperature feedback loop is used to configure the bias supply to automatically compensate for temperature fluctuations across the operating temperature range. If a constant overvoltage is maintained, most parameters, such as gain, PDE and timing will remain the same as at room temperature.

Dark Count Rate (DCR), will also increase with increasing temperature. At elevated temperature a higher DCR will still be observed regardless of bias compensation. Since DCR will also decrease at lower temperatures active cooling of the SiPM may be employed as a method to reduce SiPM noise.