Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
  • G01J1/44—Electric circuits
  • G01J1/46—Electric circuits using a capacitor
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J1/00—Photometry, e.g. photographic exposure meter
  • G01J1/42—Photometry, e.g. photographic exposure meter using electric radiation detectors
  • G01J1/44—Electric circuits
  • G01J2001/4446—Type of detector
  • G01J2001/446—Photodiode
  • G01J2001/4466—Avalanche

Definitions

• the invention relates to a device for detecting electromagnetic radiation.
• Devices for detecting electromagnetic radiation can be used to observe a scene emitting very little light.
• the management of a very weak light signal during a more or less short period imposes many technical constraints on the detection circuit.
• the detection of a low luminous flux and its retranscription into an exploitable electric current are associated with the use of avalanche photodiodes.
• the avalanche photodiodes are strongly polarized, that is to say beyond the avalanche voltage, which makes it possible to generate a large electric current when a first light photon is detected. Once the avalanche is completed, the polarization is reduced and it is necessary to wait for a certain time to defuse the avalanche.
• a detection device with photodiodes Avalanche can not be used for the detection of photons emitted with a short interval. Indeed, during the detection of the first photon, there is triggering of the avalanche and production of an intense electric current. During the passage of the current, electric charges are trapped in the different layers of electrically insulating materials that form the photodiode which temporarily disrupts the operating characteristics of the photodiode for the detection of future photons.
• detection devices using avalanche photodiodes are slow recovery devices. It is necessary to pass the trapped charges in order to have repeatable measurements.
• the photodiode In order to limit the trapping of electrical charges in the photodiode, it is possible to operate the photodiode slightly below the avalanche threshold. Under these conditions, there is no initiation of the avalanche. In this configuration, the photodiode has a detection gain which is defined by the applied bias. The set of voltage applied makes it possible to define the conversion efficiency of the photodiode. In this case, there is also polarization of the photodiode with high voltages. Important constraints exist on the reading circuit to be able to increase the sensitivity of the circuit and to improve the detection threshold of the photons.
• the photodetector is connected on the one hand to a read circuit which stores the charges emitted by the photodetector and on the other hand to a bias circuit via a resistor.
• this resistor is a discrete resistor connected to the reading circuit which is not optimal. As indicated in document D1, this configuration does not make it possible to form a compact device and the integration of a possible integrated resistor is also indicated as incompatible with standard constraints of compactness.
• Document FR 2857545 proposes to replace this discrete resistor with a diode-mounted MOS transistor.
• a read circuit coupled to a first terminal of the photodetector, the read circuit being configured to transform a current signal emitted by the photodetector into a voltage signal
• a capacitor having a first terminal electrically coupled to the first terminal of the photodetector and a second terminal electrically coupled to the read circuit
• a bias circuit configured to bias the photodetector during a first period of time by means of a first bias condition, the bias circuit being configured to leave the first terminal of the photodetector at a floating potential in a second period of time, the first polarization condition being configured to operate the photodetector in a linear avalanche regime during the second period of time,
• a resistor having a first terminal electrically coupled to the bias circuit and a second terminal electrically coupled to the first terminal of the photodetector.
• FIG. 1 schematically represents a detection circuit according to the prior art
• FIG. 2 schematically represents an embodiment of a detection circuit according to the invention
• FIG. 3 schematically represents a particular embodiment of a detection circuit according to the invention.
• the detection device comprises a photodetector 1 schematized in the form of a current source, capable of converting the received light signal into an electrical signal.
• the photodetector 1 is configured to detect electromagnetic radiation in a specific range of wavelengths.
• the photodetector 1 may be formed by any suitable device, for example by a photodiode or by a quantum well or multi-quantum well device.
• the photodetector is a polarized device with a first voltage range for delivering information representative of the observed scene.
• the photodetector is advantageously configured to detect infrared radiation, preferably a particular range of infrared radiation, for example ranges, LWIR, MWIR or SWIR.
• the photodetector 1 has a first terminal electrically coupled to a read circuit 2.
• the read circuit 2 is configured to transform a current signal that arrives at an input terminal into a voltage signal Vs at its output terminal.
• a capacitor 3 is connected between the first terminal of the photodetector 1 and the input terminal of the reading circuit 2.
• the reading circuit 2 imposes a read voltage on the capacitor 3.
• the capacitor 3 prevents the potential present on the photodetector 1 to reach directly the reading circuit 2. The same applies to the potential applied by the reading circuit 2.
• the detection device also comprises a polarization circuit 4 configured to bias the photodetector 1.
• the polarization circuit 4 is configured so that the photodetector 1 acts as a current source whose current intensity is a function of the electromagnetic radiation received.
• the detection device is configured to detect a signal of very low intensity.
• the bias circuit 4 is configured to bias the photodetector 1 into its desired operating mode. Since the bias circuit 4 is electrically coupled to the photodetector 1, it is configured not to completely absorb the emitted electrical signal, advantageously to periodically absorb the emitted signal.
• the bias circuit 4 and the reading circuit 2 are connected to or coupled to the photodetector 1 so as to define two distinct paths for the flow of the current emitted by the photodetector 1.
• the polarization conditions are configured to place the photodetector 1 above the avalanche threshold or slightly below the avalanche threshold (in absolute value) to have a linear avalanche detector.
• each received photon generates a predefined quantity of electrons.
• This quantity of electrons is defined by the polarization conditions of the photodetector. In this way, the detection of a photon generates a value fixed electron and the detection of two photons generates a value twice as large as the detection of a single photon.
• the polarization conditions are chosen so as to have a gain of between 5 and 200 and more particularly between 10 and 150.
• the bias circuit 4 is configured to impose a first potential difference across the photodetector 1 for a first period of time.
• the polarization circuit 4 is advantageously electrically coupled to the terminals of the photodetector 1.
• a first potential for example a substrate potential V S UB, is applied to the second terminal of the photodetector 1.
• a second potential, for example a bias potential is applied to the first terminal of the photodetector 1 via a resistor R.
• the resistor R allows the electrical coupling between the bias circuit 4 and the photodetector 1.
• the photodetector is polarized.
• the resistor used is not intended to maintain the polarization in case of detection of photons.
• the resistor is configured to protect the detection device in the case where the photodetector is short-circuited by avoiding the injection of an excess current into the substrate. In case of detection, part of the signal is absorbed by the bias circuit 4.
• the resistor R has a first terminal electrically coupled to the first terminal of the photodetector 1 and the capacitor 3.
• the resistor R has a second terminal electrically coupled to a voltage source 5 so that electric charges can flow between the bias circuit 4 and the photodetector via the resistor R.
• the voltage source 5 delivers a fixed potential.
• the bias circuit 4 is electrically coupled to the second terminal of the resistor R.
• the bias circuit 4 is configured to bias the photodetector 1 for a first period of time via the resistor R. In a mode of In a particular embodiment illustrated in FIG. 3, the bias voltage V RE F is applied by a voltage source 5 during the first period.
• the bias voltage V RE F OR a voltage that arises is applied to the first terminal of the photodetector 1 through the resistor R.
• the voltage applied to the second terminal is used to set the polarization conditions.
• the voltage applied to the second terminal is for example a substrate voltage Vsub.
• the bias voltage V RE F is no longer applied to the photodetector 1.
• the first terminal of photodetector 1 is left at floating potential.
• the polarization of the photodetector is maintained by means of the electrical capacitances and in particular by means of the parasitic capacitance of the photodetector 1. This embodiment is particularly easy to achieve with a photodiode as a photodetector.
• the detected photons are transformed into electric charges which are integrated in the capacitor 3.
• the bias circuit 4 comprises a switch 6 connected between the source of voltage
• the photodetector 1 is biased by the voltage source 5 when the switch 6 is in the closed state.
• the switch 6 is controlled by BIAS signal generator.
• the BIAS signal makes it possible to control the opening and closing of the switch and therefore the application of the bias voltage or not. In the first period, the switch
• the switch 6 is closed. During the second period, the switch 6 is open. During the second period, the voltage source 5 does not intervene in the polarization of the photodetector 1.
• the switch 6 is a transistor and preferably a field effect transistor.
• the current does not flow in the resistor R, it is integrated in the capacitor 3.
• the capacitor 3 transmits current information relative to the signal generated by the photodetector 1.
• the reading circuit 2 thus receives a current signal representative of the scene observed.
• the current emitted by the photodetector 1 flows through the capacitor 3.
• a first voltage range may be present on one side of the capacitor 3, for example in the portion containing the photodetector.
• a second voltage range may be present on the other side of the capacitor 3, for example in the part containing the reading circuit 2. It is advantageous to apply a first polarization across the photodetector which is uncorrelated to a second polarization applied to the terminals of the reading circuit 2.
• the value of the first polarization is set independently of the value of the second polarization.
• This type of circuit makes it possible to apply high voltages across the photodetector 1 while having lower voltages at the terminals of the reading circuit 2. It is then possible to combine a highly polarized photodetector to be very sensitive to the incident radiation and a reading circuit less strongly polarized so as to be very sensitive to the electrical signal arriving at the input and to present a low electronic noise.
• the reading circuit 2 is an integrating reading circuit which comprises an integration capacitor C in t.
• the integration capacitor C in t is arranged to store the electrical charges emitted by the photodetector 1.
• the integration capacitor C im is mounted in feedback of an amplifier 7.
• a reset circuit 11 may be used to initialize the integration capacitor Cj nt by shorting its electrodes.
• the short circuit signal res and and the signal 3 ⁇ 4IAS are linked.
• the two signals are configured to reset the read circuit integration capacitor when the bias circuit 4 biases the photodetector 1.
• the two signals are synchronized, in phase or in phase opposition.
• the capacitance of the capacitor 3 is greater than the capacitance of the integration capacitor of the reading circuit 2.
• the capacitance of the capacitor 3 is at least twice as large as the capacitance of the integration capacitor of the reading circuit 2.
• the capacitance of the capacitor 3 is equal to 100 fF and the capacitance of the integration capacitor dm is equal to 30 fF.
• the capacitance of the capacitor 3 is preferably greater than the electrical capacitance of the parasitic capacitor of the photodetector and even more preferably at least twice the electrical capacitance of the parasitic capacitor of the photodetector.
• the reading circuit 2 is a transimpedance amplifier circuit which comprises an amplifier 7 with an integration capacitor Cmt connected in feedback as shown in FIG. 2.
• the reading circuit 2 is formed on a first monoblock substrate of semiconductor material which makes it easy to produce a compact and efficient circuit.
• the substrate may be a solid semiconductor substrate or the active layer of a semiconductor on insulator substrate. It is advantageously the same for the bias circuit 4 which can be made on the same substrate as the read circuit.
• the bias circuit and / or the read circuit comprise a plurality of transistors which are formed in the semiconductor material substrate. These transistors are electrically insulated from one another by means of insulating patterns which sink into the semiconductor substrate.
• the insulation patterns are made of an electrically insulating material. The thickness of these insulation units is advantageously greater than 50 nm advantageously to 100 nm.
• the transistors of the read circuit 2 and / or the bias circuit 4 are formed on the one-piece substrate made of semiconductor material and the resistor R is produced outside this substrate.
• the resistor R is separated from the substrate by an electrically insulating layer.
• the electrically insulating layer is advantageously the layer used to form the insulation patterns.
• the resistor R is produced by means of a polysilicon pattern.
• the read circuit 2 is formed on a one-piece substrate of semiconductor material which makes it easy to produce a compact and efficient circuit.
• the substrate may be a solid semiconductor substrate or the active layer of a semiconductor-on-insulator substrate.
• the transistors of the reading circuit 2 are formed on the one-piece substrate made of semiconductor material and the capacitor 3 is made out of this substrate.
• the capacitor 3 is separated from the substrate by an electrically insulating layer.
• the capacitor 3 is made by means of two electrodes which are each formed by a semiconductor or metal material which are separated from the substrate by an electrically insulating film.
• This particular configuration makes it possible to compact a capacitor 3 which is electrically decoupled from the substrate, which enables it to withstand high voltages without risking a parasitic transit of charge carriers inside the substrate.
• the electrode of the capacitor 3 in contact with the photodetector 1 is separated from the substrate by an electrically insulating film.
• the other electrode of the capacitor is formed in the substrate and possibly by a source / drain electrode or gate of one of the transistors forming the input terminal of the read circuit.
• the use of passive elements made outside the semiconductor substrate makes it possible to increase the reliability of the separation between the high voltage zone applied on one side of the capacitor 3 and the low voltage zone applied on the other side of the capacitor 3. , here in the semiconductor substrate. It is then possible to have in the same circuit, part of the components subjected to high voltages and another part of the components subjected to a lower voltage while avoiding parasitic transfer of the charge carriers via the substrate.
• the dielectric material present between the two electrodes of the capacitor 3 makes it possible to avoid large leaks of current.
• the resistor R is arranged to form a parasitic capacitor Cmti connected to the reading circuit 2. This arrangement makes it possible to increase the conversion gain of the integrating reading circuit 2 while reducing the noise. More specifically, the resistor R may be arranged so as to form an electrical capacitance C in t provided with an electrical connection connecting the input of the amplifier 7 with the output of the amplifier 7 to form a capacitor. integration of the reading circuit 2 through the capacitor 3.
• the parasitic capacitor Cmti is connected by feedback of the amplifier 7 of the reading circuit 2.
• the second input of the amplifier can be connected to a voltage source which applies a reference voltage V RE F2- The reference voltage is then applied to one electrode of the capacitor 3 and the bias voltage is applied to the other electrode.
• the reference voltage VREF2 contributes to the initialization of the polarization of the capacitor 3 during the first period when the switch 6 is in the closed state.
• the capacitor 3 is arranged to form a parasitic capacitor Cj nt 2 connected to the reading circuit 2.
• This arrangement makes it possible to increase the gain of converting the readout circuit 2 integrator while reducing the noise.
• the parasitic capacitor Cj n t2 is connected in feedback against the amplifier 7 of the read circuit 2.
• a voltage blocking circuit 8 is connected to the second terminal of the resistor R.
• the blocking circuit 8 is configured to block the voltage present on the second terminal of the resistor R to a threshold value.
• the blocking circuit 8 is configured to deliver a feedback current which freezes the voltage of the second terminal of the resistor R to a threshold value.
• the blocking circuit is particularly advantageous during the second period of time. If the photodetector is short-circuited, the blocking circuit 8 limits the current flowing which protects the read circuit.
• the blocking circuit 8 comprises an additional voltage source 9 electrically coupled to the second terminal of the resistor R by means of an additional switch T1.
• the blocking circuit 8 is configured so that the additional voltage source 9 delivers a feedback current when the additional switch T1 becomes on.
• the additional switch T1 delivers a negative feedback current which makes it possible to freeze the voltage of the second terminal of the resistor R when the switch T1 becomes on.
• the switching of the switch T1 to the closed state according to the voltage value present on the second terminal of the resistor R can be achieved in different ways.
• the switch T1 is a transistor.
• the control terminal of transistor T1 is connected to another voltage source 10 which applies the clamping voltage V c i am p.
• V c i am p the clamping voltage
• the transition of the transistor T i between the states blocked and switched on is conditioned by the voltage difference that exists between the voltage present on the second terminal of the resistor R and the blocking voltage V c i am p- It is the value of the blocking voltage V C iam P which sets the value of the threshold.
• This advantageous configuration makes it possible to limit the amplitude of the voltage variations on the second terminal of the resistor R. This specificity makes it possible to protect the reading circuit and / or the bias circuit in the event of excessive voltage variation.
• the transistor is configured to operate in linear mode and not in commutation.
• a radiation detector which comprises a plurality of detection circuits as described above.
• the method of manufacturing the photodetectors is such that there is always at least one defective photodetector in a large detector. Radiation detectors using a large number of photodetectors are very difficult to achieve because an electrical fault present on a photodetector will cause a failure of the entire array of photodetectors. The strong bias applied to the photodetector in short-circuit will be present on all the reading circuits that are not configured to handle such polarization levels. This type of problem is not treated in the architecture disclosed in the document FR2857545. Indeed, it is observed that the polarization voltage of the photodetector derives from the bias voltage of the read circuit and therefore the read circuit is configured to support the bias voltage applied to the photodetector.
• the photodetectors are all highly polarized.
• a substantial current is applied continuously or quasi-continuously to the bias circuit 4, which can distort the polarization conditions applied to the other photodetectors.
• Use resistance between the photodetectors 1 and the readout circuits 2 makes it possible to reduce the current that can circulate and to retain the functionality of the other photodetectors.
• the value of the resistance is greater than 100 kOhms, which makes it possible to withstand various operating conditions, for example between 100 kOhms and 1 MOhms.
• the output terminal of the detection circuit is intended to be connected to an analysis circuit (not shown).
• This type of detection circuit allows efficient and good quality measurement on light signals having a low flux.
• This type of detection circuit is particularly well suited for linear sub-photonic detection, that is to say for counting photons.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Light Receiving Elements (AREA)
• Photometry And Measurement Of Optical Pulse Characteristics (AREA)

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• 2013
  • 2013-02-26 FR FR1300442A patent/FR3002630B1/fr active Active
• 2014
  • 2014-02-26 WO PCT/FR2014/000047 patent/WO2014131953A1/fr active Application Filing
  • 2014-02-26 US US14/770,688 patent/US9784612B2/en active Active
  • 2014-02-26 EP EP14711550.5A patent/EP2962077A1/de not_active Withdrawn

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