EP3398407A1

EP3398407A1 - Integrated circuit intended for insulation defect detection and having a conductive armature

Info

Publication number: EP3398407A1
Application number: EP16826103.0A
Authority: EP
Inventors: Bertrand Chambion
Original assignee: Commissariat a lEnergie Atomique CEA; Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Current assignee: Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
Priority date: 2015-12-28
Filing date: 2016-12-15
Publication date: 2018-11-07
Also published as: FR3046247B1; FR3046247A1; US20190369157A1; WO2017115027A1; US10845405B2

Abstract

The invention relates to an electronic circuit (1) including: an electronic component (11), a conductive armature (4) surrounding the electronic component, an electrical insulator (5) between the electronic component (11) and the conductive armature (4), a device (7) configured to measure the current passing through the armature (4) or the voltage on said armature or on the electronic component, and a defect determination device (8) configured to determine a defect in the electrical insulator (5) on the basis of the measured current or voltage.

Description

INTEGRATED CIRCUIT FOR DETECTING AN INSULATION FAULT WITH CONDUCTIVE FRAME

The invention relates to electronic circuits comprising conductive reinforcements and, in particular, electronic circuits for detecting a malfunction by a lack of electrical insulation between an electronic component of the electronic circuit and a conductive reinforcement surrounding this component.

Electronic circuits comprising arrays of light-emitting diodes or LEDs are known. Electroluminescent diodes are experiencing a significant development, in particular because of reduced power consumption, a long life deemed high, and a good integration ability for electronic circuits. The ability to integrate such LEDs has the reverse side to prevent the replacement of an LED cell in the matrix. In addition, a complete failure of one LED cell may affect the operation of all other LED cells with which it can be connected in series.

Various modes of malfunction are known for LED cells, these malfunctions sometimes being specific to the manufacturing technology of these LED cells. Progressive degradations occur in particular with the increase of the leakage currents at the junctions of the diodes or through layers of insulation. Thus, even if an LED cell remains functional, the light flux it emits gradually decreases for a given voltage level applied to its terminals.

To answer these problems, in particular for the respect of safety standards, there is a need for a solution for prior monitoring of the operation of the LEDs cells. Moreover, the analysis of the malfunction mode is sometimes rather incomplete.

Document US2015 / 0021629 describes the fixing of an array of LEDs on the substrate of a control module, and thus forming an electronic circuit. The LEDs are soldered to a conductive and rectangular metal plate. The LEDs are in electrical contact with this metal plate. The voltage of the LEDs is measured to determine a progressive shifting of the voltage level to ensure a brightness level.

This document does not guarantee optimal insulation of the LEDs, nor does it detect an insulation failure of these LEDs.

Document FR3009474 describes a matrix of LEDs in series / parallel. In order to avoid a malfunction of the lighting of a vehicle, a functional failure is detected for an LED, then it is short-circuited by a current source which guarantees a balance of current between different branches in parallel. Lighting of the remaining LEDs in the branch with a faulty LED is ensured. This document thus describes a detection of a fault by analyzing the voltage across an LED.

US2014 / 0084941 discloses a matrix of LEDs of a screen, provided with a device for testing dysfunction. The document describes a DFL detection line offset laterally with respect to the LEDs. An electrical insulator is interposed between the detection line and pixel feed tracks.

This document does not guarantee optimum insulation of the LEDs, or to detect an insulation failure of these LEDs or between these LEDs.

The invention aims to solve one or more of these disadvantages. The invention thus relates to an electronic circuit, as defined in appended claim 1.

The invention also relates to the variants detailed in the dependent claims. It will be understood by those skilled in the art that each of the features of the variants of the dependent claims may be independently combined with the features of claim 1, without necessarily constituting an intermediate generalization.

The invention also relates to a method for determining a defect of an electrical insulator, as defined in the appended claims.

Other characteristics and advantages of the invention will emerge clearly from the description which is given hereinafter, by way of indication and in no way limitative, with reference to the appended drawings, in which:

FIG 1 is a cross sectional view of an integrated circuit according to an exemplary embodiment of the invention;

FIG. 2 is a sectional view from above of the integrated circuit of FIG.

1;

FIG 3 is a current / voltage diagram illustrating the aging of a multi-chip LED connected in series, partly related to a degradation of the insulation;

FIGS. 4a and 4b are equivalent electrical diagrams for the association of LEDs connected in series and of an armature, in the case of normal operation, and in the case of a short circuit to the armature; FIG. 5 is an equivalent electrical diagram for the association of LEDs connected in parallel and of an armature;

FIG. 6 illustrates components of a matrix, tested sequentially; FIG. 7 is a diagram illustrating different cases of leakage resistance;

FIG 8 is a cross sectional view of an integrated circuit according to another exemplary embodiment of the invention.

Figures 1 and 2 are sectional views of an exemplary integrated circuit 1 according to an exemplary embodiment of the invention. The integrated circuit 1 comprises several electronic components 1 1 to 16, in this case light-emitting diodes or LEDs with nanowires. Each of the LEDs 1 1 to 16 forms an emitting pixel. The LEDs 1 1 to 16 are here formed in and on a semiconductor substrate 91. The substrate 91 is delimited into different parts separated by vertical trenches. The vertical trenches pass through the substrate 91 from one side to the other, so that the different parts of the substrate 91 are physically separated from each other. The different parts of the substrate 91 correspond to LEDs 1 1 to 16 respectively.

The integrated circuit 1 further comprises a conductive armature 4 surrounding the LEDs 1 1 to 16. The conductive armature 4 is at least partially housed in the separation trenches between the different parts of the substrate 91. The integrated circuit 1 further comprises an electrical insulator 5. The electrical insulator 5 is at least partially housed in the separation trenches between the different parts of the substrate 91. The electrical insulation 5 covers in particular the lateral faces of the various parts of the substrate 91. Thus, in section in the plane of the substrate 91, between two parts of the substrate 91, there is a layer of electrical insulation 5, the armature 4, and another layer of the electrical insulation 5. The electrical insulation 5 form on the one hand an electrical insulation between the armature 4 and the LEDs 1 1 to 16. A side face 51 of the electrical insulation 5 forms in particular a separation between the LED 1 1 and the armature 4. A side face 52 of the electrical insulation 5 forms a separation between the LED 12 and the armature 4. The electrical insulation 5 forms on the other hand an electrical insulation between the various LEDs 1 1 to 16.

The LEDs 1 1 to 16 may have a structure known per se. The LEDs 1 1 to 16 here comprise respective electrodes, positioned under the substrate 91. The LEDs 1 1 to 13 respectively comprise lower electrodes 21 to 23 disposed under their respective portion of substrate 91, and typically made of metal. The substrate 91 is made of semiconductor material. The substrate 91 is for example sufficiently doped to be conductive. The Substrate material 91 may be selected to promote the growth of LED nanowires in an organized manner. The substrate 91 is surmounted by an insulating layer 92. This insulating layer 92 is for example made of silicon oxide or silicon nitride. This layer 92 may typically comprise a thickness of between 25 nm and 25 μm.

Each of the LEDs 1 1 to 16 comprises several pins 1 1 1 passing through the thickness of the insulating layer 92. The pads 1 1 1 are intended to conduct the respective polarizations of the lower electrodes to the son of the various LEDs 1 1 to 16. The For example, studs 11 are made of a III-N alloy, for example GaN. The pads 1 1 1 may for example be made of unintentionally doped GaN or GaN type doping.

A respective wire is formed in line with each of the pads 1 1 1. The structure of the son will be described with reference to the LED 1 1, the LEDs 12 to 16 may have a similar structure. A wire comprises an amount 1 12 in contact with a stud 1 1 1 at its lower part. The amount 1 12 can be produced in a manner known per se in a III-N alloy, for example N-type doping GaN or unintentionally doped type. The amount 1 12 is covered in a manner known per se by a quantum well structure 1 13. The structure 1 13 here comprises an alternation of layers (for example alternating layers of undoped GaN and layers of InGaN). Most of the light radiation of the LED is generated in the quantum well structure 1 13. The quantum well structure 1 13 is covered in a manner known in either by a layer 1 14, for example P-doped GaN, so as to form a PN or P-N junction with the upright 1 12 or the quantum well 1 13.

The son of the LED 1 1 are covered by a conductive layer 31 forming an upper electrode. The layer 31 is conductive in order to be able to electrically polarize each P-N junction. The conductive layer 31 is transparent for the emission wavelength of the LED 1 1. The layer 31 can be made in a manner known per se indium tin oxide (usually designated by the acronym ITO) or aluminum doped zinc oxide.

A power supply circuit (not shown) makes it possible to selectively apply a potential difference of an appropriate amplitude between the lower electrode 21 and the layer 31 of the upper common electrode, in order to obtain a light emission by the LED. 1 1.

The electronic circuit 1 according to the invention comprises a device 7 configured to measure the current flowing through the armature 4, the voltage on this armature 4 or on each of the LEDs 1 1 to 16. The device 7 is for example implemented under the form of a microcontroller. The electronic circuit 1 further comprises a device 8, connected to the device 7. The device 8 is configured to determine a fault of the electrical insulator 5 as a function of the voltage or current measured by the device 7. As detailed more precisely in FIG. practical examples thereafter, the device 8 can anticipate or see a malfunction of the electronic circuit 1. The device 8 is for example implemented in the form of a microcontroller.

In the particular example illustrated, the conductive reinforcement 4 is advantageously made of doped polysilicon. The polysilicon may for example be doped with a concentration of at least than 10 ¹⁹ CNRR ^3, preferably at least 5 ^* 10 ¹⁹ cm ^"3, to form an armature 4 with little residual thermomechanical stresses after fabrication. A such doped polysilicon thus forms an inexpensive filling material for the reinforcement 4. The doped polysilicon has mechanical properties similar to those of the doped silicon substrate 91 (having for example a dopant concentration of the same order of magnitude as the reinforcement 4), during a rise in temperature In such a configuration, the mechanical stresses in the armature 4 are reduced during a rise in temperature linked for example to the formation of silicon oxide layers by thermal oxidation or during annealing of a layer of the LEDs, or during any other step of a manufacturing process that may involve significant heating, and potentially mechanical constraints between frame 4 and substrate 91.

Figure 3 is a representative diagram of an example of aging of a multi-chip LED connected in series. The diagram shows on the ordinate the current flowing through the LED, and on the abscissa the potential difference applied across the LEDs. The voltage Vm corresponds to the minimum voltage for stimulating the spontaneous emission in the junction (light emission) of the LED. The curve in solid line corresponds to a new LED, the curve in dashed line corresponds to an LED after 5000 hours of operation.

The potential difference Vm corresponds to the minimum voltage to obtain an ignition of the light emitting diode. It is generally found that the current flowing for a bias lower than Vm increases as a function of time. It can be seen that the leakage current flowing through the LED, powered by a potential difference of less than Vm, is much higher for the LED having undergone a certain period of use. An insulation fault with a conductive frame 4 surrounding the LED may be an important factor in such a leakage current. The structure illustrated in FIGS. 1 and 2 can be used, for example, to connect the LEDs 1 1 to 16 in series, in parallel, or according to a time-multiplexed matrix, as a function of the interconnections made between the different electrodes of these LEDs 1 1 to 16 .

Figures 4a and 4b are equivalent electrical diagrams of several LEDs 1 1 to 14 connected in series. The armature 4 is comparable to a first conductive plate of several capacities 45. The insulation 5 of the armature 4 can be modeled as the insulation of these capacitors 45. Each connection node between the LEDs can be likened to a second plate Conducting capabilities 45.

As illustrated in FIG. 4a, during normal operation, the armature 4 (and therefore the first conductive plates of the capacitors 45) is placed at a floating potential. The first conductive plates of the capacitors 45 are thus isolated from the second conductive plates by means of the insulator 5.

FIG. 4b illustrates an example of a malfunction, materialized by a short circuit between the armature 4 and the connection node of the LEDs 12 and 13. The armature 4 is then brought to the potential of this connection node. The armature 4 must thus have a floating potential in normal operation. This floating potential must take a value corresponding to the average of the potentials applied across the LEDs. In case of short-circuit through the insulation 5, between the armature 4 and an LED (more precisely its substrate or one of its electrodes), the armature 4 then takes the potential of this LED. The device 7 is connected to the armature 4 and measures the potential of the armature 4. The device 7 supplies the potential measured to the device 8. Depending on the value of the potential measured by the device 7, the device 8 can:

-determining an abnormal deviation of the floating potential, representative of a failure of the insulator 5;

-Locate with which LED the insulator 5 has a failure inducing a connection to the frame 4.

The location of the LED for which the insulator 5 has a fault can be performed as follows: either p the number of LEDs connected in series, and either Vf the ignition potential difference applied to each LED, it can be deduced that the Potential difference applied across the entire chain of LEDs in series is Vin = p * Vf. In normal operation, the armature 4 is at a floating potential V4 "Vin / 2. If the measured potential Vm takes this value V4, the device 8 determines that the armature 4 is at its normal potential and therefore that the insulator 5 has a priori no fault.

If the measured potential Vm differs significantly from V4, the device 8 determines a failure of the insulator 5. The position of the faulty LED in the string of LEDs connected in series will be identified by an index k, this index position k being determined from the potential of mass up to the potential Vin. The index k is defined by k = Vm / Vf, rounding the value of k found to the nearest integer.

With the potential Vm measured for the application of the voltage Vin on the chain of LEDs in series, it is possible to realize the determination of a fault during the use of the LEDs. Such a test can also be performed at the output of the production line, by applying the voltage Vin, in order to avoid having to carry out an optical check of the integrated circuit 1.

In the case where the measured voltage Vm is V4, this measurement can either correspond to a floating potential for normal operation, or to an insulation fault for the LED of index k = p / 2. In order to discriminate between these two cases, one can dynamically analyze the evolution of the voltage Vm during the application of a step of the voltage Vin on the chain of LEDs connected in series.

It is also possible to measure a current flowing through the armature 4 to the measuring device 7. The amplitude of this current may be representative of the leakage impedance of the insulator 5, and therefore of the amplitude of the defect. insulation 5.

Figure 5 is an equivalent electrical diagram of several LEDs connected in parallel in a matrix, in the absence of malfunction.

The armature 4, a common electrode of the LEDs 1 1 to 14 and the insulator 5 can be modeled as a capacitor 45. The armature 4 forms a conductive plate at a floating potential in normal operation.

The armature 4 must have a floating potential during normal operation.

This floating potential must take a value Vf / 2, corresponding to half the potential Vf applied across the LEDs. In case of a short-circuit through the insulation 5, between the armature 4 and an LED (more precisely its substrate or one of its electrodes), the armature 4 then takes the potential Vf or mass.

The device 7 is connected to the armature 4 and measures the potential of the armature 4.

The device 7 supplies the measured potential to the device 8. Depending on the value of the potential measured by the device 7, the device 8 can determine an abnormal deviation of the floating potential, representative of a failure of the insulator 5.

In the case of an array of matrix LEDs powered with time division multiplexing, a capacitor 45 is sequentially connected in parallel with each powered LED. The test mode that will be described can also be used for an integrated circuit 1 provided with a set of LEDs connected in parallel, if this integrated circuit 1 is configured to sequentially supply each of the LEDs.

FIG. 6 illustrates a configuration of an integrated circuit 1 in which each LED 10 is connected to the intersection between a line track and a column track. Thus, each LED 10 comprises an electrode connected to a line track and an electrode connected to a column track. A line control circuit 61 is connected to lines 1 to m. The control circuit 61 selectively applies a first supply potential (for example a ground potential) on one of the lines and keeps the other lines in a floating state. Column control circuit 62 is connected to columns 1 to n. The control circuit 62 selectively applies a second supply potential (the potential Vf) on one of the columns and keeps the other columns in a floating state.

By appropriate control of the control circuits 61 and 62, the insulation between each of the LEDs 10 and the armature 4 can be sequentially tested. Thus, for each of the LEDs 10 powered, the potential Vm can be measured. By identifying whether the potential Vm is equal to Vf / 2 or Vf for each of the LEDs 10, it is possible to determine whether its insulation with respect to the armature 4 is deteriorated or not. Since the position of the LED during power supply is known, the location of a possible defect of the insulator 5 is known.

It is also possible to predict a malfunction by measuring, for example, a leakage current passing through the armature 4. Depending on the amplitude of the leakage current passing through the armature 4, it is possible to anticipate an interruption of service of an LED. or the electronic circuit 1. Thus, if the amplitude of the leakage current exceeds a threshold, it can be determined that the residual life of an LED is reduced, and that compliance with safety standards requires its replacement or preventive measures.

Figure 7 is a diagram illustrating different cases of leakage resistances that can be determined. For example, it is conceivable to determine the leakage resistance through the frame 4. By considering the frame 4 to its floating potential as a voltage source, it can be connected to the mass successively by means of several different calibrated resistors, in order to calculate its internal resistance. By measuring the drained currents of the armature 4 for these two resistance values and by measuring the potential on the armature 4, it is possible to extrapolate diagrams as illustrated, representing the potential Vm as a function of the drained current. The leakage resistance can be deduced as a function of the slope of these characteristics. The solid line curve corresponds, for example, to a quasi-zero leakage resistance towards the armature 4, that is to say a free short-circuit between an LED and the armature 4. The curve in dashed line corresponds to a higher leakage resistance to the frame 4.

The foregoing embodiment has been illustrated with reference to nanowire LEDs. Figure 8 is a cross-sectional view of an integrated circuit 1 according to another embodiment of the invention. The integrated circuit 1 comprises several LEDs according to another design. Each of the LEDs 1 1 to 13 forms an emitting pixel.

The integrated circuit 1 further comprises a conductive reinforcement 4 surrounding the LEDs 1 1 to 13. The integrated circuit 1 further comprises an electrical insulator 5. The electrical insulator 5 on the one hand forms an electrical insulation between the armature 4 and the LEDs 1 1 to 13. A side face 51 of the electrical insulation 5 forms in particular a separation between the LED 1 1 and the armature 4. A side face 52 of the electrical insulation 5 forms a separation between the LED 12 and the armature 4. The electrical insulation 5 on the other hand forms an electrical insulation between the various LEDs 1 1 to 13.

The LEDs 1 1 to 13 may have a structure known per se. The

LEDs 1 1 to 13 here comprise respective electrodes. The LEDs 1 1 to 13 respectively comprise lower electrodes 21 to 23 typically made of reflective metal. The electrodes 21 to 23 are each covered with a P-doped semiconductor layer 1 16 (for example P-doped GaN) with which they are in contact. The semiconductor layer 1 16 is covered with an N-type doped semiconductor layer 1 18 (for example N-type doped GaN). An active layer 1 17 is formed at the interface between the layers 1 16 and 1 18. The superposition of the layers 1 16 to 1 18 will here be assimilated to a substrate. The superposition of the layers 116 to 18 forming a substrate is delimited into different parts separated by vertical trenches. The vertical trenches pass through the superposition of layers from one side to the other, so that the different parts of the substrate are physically separated from each other. The conductive reinforcement 4 is at least partially housed in the separation trenches between the different parts of the substrate. The electrical insulation 5 is at least partially housed in the separation trenches between the different parts of the substrate. The electrical insulation 5 covers in particular the lateral faces of the different parts of the superposition of layers 1 16 to 1 18. Thus, in section in the plane of the substrate formed, between two parts of the substrate, there is a layer of electrical insulation 5 , armature 4, and another layer of electrical insulation 5.

The active layer 11 may in particular comprise one or more quantum wells. The LEDs 1 1 to 13 comprise respective upper electrodes 31 1 to 313 formed in contact on the layer 1 18. The LEDs 1 1 to 13 can thus be polarized via their respective lower and upper electrodes. The electrodes 31 1 to 313 are transparent for the emission wavelength of their respective LEDs. The electrodes 31 1 to 313 are for example made of tin indium oxide.

The electronic circuit 1 according to this embodiment also comprises a device 7 configured to measure the current flowing through the armature 4, the voltage on this armature 4 or on each of the LEDs 1 1 to 13. The device 7 is for example implemented. in the form of a microcontroller.

The electronic circuit 1 further comprises a device 8, connected to the device 7. The device 8 is configured to determine a fault of the electrical insulator 5 as a function of the voltage or current measured by the device 7. As detailed more precisely in FIG. practical examples thereafter, the device 8 can anticipate or see a malfunction of the electronic circuit 1. The device 8 is for example implemented in the form of a microcontroller. The mode of identifying and locating a malfunction may be similar to that described with reference to the first embodiment.

In order to anticipate a malfunction, it will also be possible to evaluate the drift of the floating potential of the armature 4 prior to a malfunction.

In the examples detailed above, the armature 4 is at a floating potential. It is also possible to apply a potential on the armature 4 and determine the current flowing through it.

In the context of tests in a production line, the measurements made can also be cross-checked with optical measurements in order to refine the diagnosis of the dysfunction. Although the invention has been described for a particular application to LED-type electronic components, the invention is also applicable to any other type of segmented or pixelated electronic component containing a conductive reinforcement and electrically isolated from the pixel array.

Claims

1. Electronic circuit (1), characterized in that it comprises:

a substrate (91) delimited in different parts by at least one vertical trench;

two electronic components (1 1) formed in and on respective parts of the substrate and separated by said vertical trench;

a conductive reinforcement (4) housed at least partially in said trench, and surrounding the two electronic components;

an electrical insulator (5) housed at least partially in said trench between the electronic components (1 1) and the conductive reinforcement (4);

a device (7) configured to measure the current flowing through the armature (4) or the voltage on this armature;

a fault determination device (8) configured to determine a fault of the electrical insulation (5) as a function of the measured current or voltage.

2. Electronic circuit (1) according to claim 1, wherein said armature (4) mainly includes polysilicon having a dopant concentration of at least 10 ¹⁹ cnn ^{~ 3} .

An electronic circuit (1) according to claim 1 or 2, wherein said electronic components (1 1) are light-emitting diodes.

4. An electronic circuit (1) according to any one of the preceding claims, wherein said armature (4) is at a floating potential.

An electronic circuit (1) according to any one of the preceding claims, wherein said electrical insulator (5) isolates each of said electronic components from the conductive framework and isolates said electronic components (1-16) from each other.

An electronic circuit (1) according to any one of the preceding claims, wherein said electronic components (1 1 -16) are electrically connected in series.

7. Electronic circuit (1) according to any one of claims 1 to 5, wherein said electronic components (1 1 -16) are electrically connected in parallel.

8. Electronic circuit (1) according to any one of claims 1 to 5, comprising a feed device configured to feed sequentially said electronic components (1 1 -16) with the same potential difference.

An electronic circuit (1) according to any one of the preceding claims, wherein said vertical trench passes through said substrate (91) from side to side.

A method for determining a defect of an electrical insulator (5), the method comprising the steps of:

-providing an electronic circuit (1) including an electrical insulator (5), an electronic component (1 1) and a conductive reinforcement (4) surrounding the electronic component, the electrical insulator (5) being disposed between the conductive reinforcement ( 4) and the electronic component (1 1),

measuring the current flowing through the armature (4) or the voltage on this armature or on the electronic component;

-determination of a fault of the electrical insulator (5) as a function of the measured current or voltage.

1 1. Determination method according to claim 10, wherein said armature (4) of the electrical circuit (1) is at a floating potential in the absence of fault of the electrical insulator (5).

12. Determination method according to claim 10 or 11, further comprising a step of locating the location of a fault as a function of the amplitude of the measured voltage or current.

13. Determination method according to claim 12, wherein said electronic circuit provided comprises several electronic components (1 1) electrically connected in series and surrounded by the conductive reinforcement (4), the electrical insulation being disposed between the conductive reinforcement. (4) and said electronic components (1 1), and wherein the location of the fault is achieved by measuring the voltage on said armature and comparing the measured voltage with the supply voltages of the series connected electronic components.

14. Determination method according to claim 12, wherein said circuit (1) provided comprises several electronic components (1 1) surrounded by the conductive reinforcement (4), the electrical insulation being disposed between the conductive reinforcement (4). and said electronic components (1 1), said supplied circuit comprising a power supply device configured to sequentially power said electronic components (1 1 -13) with the same potential difference, and wherein the location of the fault is realized by measuring the voltage on said armature (4) and determining for which electronic component supplied the measured voltage corresponds to a supply voltage of the electronic component.

15. Determination method according to any one of claims 10 to 14, wherein said provided armature (4) mainly includes polysilicon having a dopant concentration of at least 10 ⁹ crrr ³ .