FR2778742A1 - THERMOELECTRIC SENSOR IN PARTICULAR FOR ELECTRICAL APPLIANCES - Google Patents

Abstract

The present invention relates to a thermoelectric sensor in particular for electrical devices comprising a resistor (3) and a thermocouple (4) on a silicon substrate (2) associated with a layer (1) of an electrical and thermal insulating material which can be constituted in particular by a silicon compound, characterized in that the resistor (3) and the thermocouple (4) are deposited on a central area (12) which is joined by bridges (11) to a belt area (13) and by the causes a central silicon mass (5) thermally insulated from the substrate (2) to be placed under said central area (12).

Description

The invention relates on the one hand to a thermoelectric sensor in particular for

  electrical apparatus, comprising a resistor and a thermocouple on a silicon substrate associated with a layer of an electrically and thermally insulating material which can be

  constituted in particular by a silicon compound.

  We know for example from patent EP 615 266, a thermoelectric sensor intended for an electrical protection device, constituted by a resistance traversed by a current and by a temperature sensor, the thermal power dissipated by the resistance

  being measured by the temperature sensor.

  In the sensor which is described in IEEE Electron Devices Vol. 13, N0 7, July 1992, a polysilicon heating resistor and a polysilicon thermocouple are deposited on an electrical and thermal insulating layer of silicon compound, deposited layer

  itself on a silicon substrate.

  The object of the present invention is to provide a thermoelectric sensor produced with microelectronics technologies which has a small footprint and is provided with a thermal memory and a time constant suitable for electric motor protection devices or circuit breakers. It is likely to include, on the same substrate, integrated electronic functions. The strength of the sensor can be improved

  without reducing thermal resistance.

  The sensor according to the invention is essentially characterized in that the resistance and the thermocouple are deposited on a central area which is joined by bridges to a belt area and in that a central mass of silicon thermally

  isolated from the substrate is arranged under said central area.

  The invention will now be described in more detail with reference to embodiments given by way of examples and represented by the accompanying drawings in which: - Figure 1 is a perspective view of a first embodiment the thermoelectric sensor according to the invention; - Figure 2 is a section on I1-11 of Figure 1; - Figure 3 is a second embodiment of the sensor o it is associated with electronic circuits within a monolithic circuit;

2 2778742

  FIG. 4 is a third embodiment of the sensor according to the invention; FIG. 5 represents a first application of the sensor according to the invention in a protection device of the circuit breaker or motor starter type; - Figure 6 shows a second application of the sensor according to the invention in a protection device of the circuit breaker or motor starter type. The sensor illustrated in FIGS. 1 to 6 comprises a resistor 3 traversed by a current and a thermocouple 4, the thermal power dissipated by the resistor 3 being

measured by thermocouple 4.

  The sensor referenced 10 as a whole is produced on a silicon substrate 0 with microelectronic technologies, of CMOS, BICMOS, or bipolar type. To the

  At the end of the manufacturing cycle, there is a step of etching the silicon.

  The heating resistor 3 is deposited on a layer 1 of an electrical and thermal insulating material of the silicon compound type (Si02 or Si3N4), this insulating layer being deposited itself on a silicon substrate 2. The thermocouple 4 is also deposited on layer 1. Resistor 3 is made of polysilicon. Thermocouple 4 is made of polysilicon or another technology adapted to the support (aluminum by

example).

  The resistor 3 and the thermocouple 4 are deposited on a central area 12 which is joined by bridges 11 to a belt area 13 of the layer 1. In the embodiments of FIGS. 1 and 3, the bridges 11 join the central area 12 at the corners of the

belt 13 of layer 1.

  A silicon mass 5 is placed under the central area 12 of the layer 1.

  This mass 5 is thermally insulated from the substrate 2 and provides thermal capacity. The bridges 11 provide thermal resistances. The set has a thermal time constant proportional to the product of resistance and thermal capacity, and behaves like a first-order RC filter. The heating resistor 3 made of polysilicon is isolated from the silicon substrate by the layer 1. Likewise the thermocouple

  4 is isolated from silicon by layer 1.

3 2778742

  Wells 6 opening at the level of layer 1 extend between the bridges 11 and between the central mass 5 and the substrate belt 2. They serve to isolate, from the point of view

  thermal, the mass of silicon 5 relative to substrate 2.

  Preferably the thermocouple 4 consists of several thermocouples associated in series. The voltage delivered by the thermocouples varies with the thermal power injected into the mass 5. The hot junction is placed on track 12 while the

  cold junction is placed on the belt 13.

  The dimensions of the suspension arms and of the mass are chosen so as to achieve a compromise between the time constant, the resonance frequency, the resistance

shock from the sensor.

  In the embodiment of FIG. 3, the sensor is integrated into an electronic circuit 71 associated with the resistor 3 and to an electronic circuit 72 associated with the

thermocouple 4.

  In the embodiment of Figure 4, the sensor is stiffened by a greater number of bridges 11 than in the previous embodiment. On certain bridges, heating resistors 31 made of polysilicon are provided. The heating provided by these resistors 31 can be regulated on the bridges so that the temperature on these bridges corresponds to a positive, zero or negative gradient with respect to the temperature of the sensor. Depending on the case,

  increases the thermal resistance, it is kept or decreased.

  The thermoelectric sensor 10 which has just been described is in particular intended for use in an electrical device for protecting a load M (motor for example), of the circuit breaker type or of a motor starter, such as that illustrated in the Figure 5 or 6. The device comprises, on a current line L, a current sensor 8 which measures the current Il and provides an output current 12. In the event of a fault detection, the device protects the load M

by acting on a KM switch.

  In the embodiment of FIG. 5, the output signal 12 from the current sensor 8 is injected onto an electronic processing circuit 91 calculating the effective current of the load M to be protected. The circuit 91 delivers a current proportional to the effective current and supplying the heating resistor 3 of the sensor. The power dissipated by the resistor 3 is proportional to the square of the current and represents the thermal state of the load M to be protected. This thermal state is measured by thermocouple 4, the output signal of which is

4 2778742

  sent to electronic circuit 91 which controls the opening of the KM switch in the event of a fault. In the sensor 10, the thermal state of the load is materialized in the form of a temperature difference with respect to the ambient temperature. This temperature difference is maintained following a power supply shutdown by performing a thermal memory function by replacing the capacitance-resistance pair normally allocated to this

  function. The sensor allows a significant gain in reliability compared to the capacity-

  resistance for operation at ambient temperatures above 1 00 C.

  In the embodiment of FIG. 6, the thermoelectric sensor 10 receives ic directly the output signal 12 from the current sensor and directly calculates the thermal state of the load M to be protected. The thermocouple 4 controls an electronic circuit 92 which controls the switch KM. Sensor replaces analog electronic circuit

  or digital dedicated to the calculation of the effective current and the thermal state.

  The operation of the sensor is as follows: The circulation of a current in the resistor 3 causes the mass 5 to heat up by the Joule effect. The thermocouple 4 measures the temperature difference between the mass of silicon 5 and the substrate 2 which is at ambient temperature. Losses by convection with air can reduce thermal resistance. They are eliminated by placing the sensor under vacuum. It is understood that it is possible without departing from the scope of the invention to imagine variants and improvements in detail and even envisage the use of equivalent means.

2778742

Claims (6)

  1- Thermoelectric sensor in particular for electrical devices comprising a resistor (3) and a thermocouple (4) on a silicon substrate (2) associated with a layer (1) made of an electrical and thermal insulating material which can be constituted in particular by a compound of silicon, characterized in that the resistor (3) and the thermocouple (4) are deposited on a central area (12) which is joined by bridges (11) to a belt area (13) and in that a central mass of silicon (5) thermally isolated from the   substrate (2) is arranged under said central area (12).   2. Sensor according to claim 1, characterized in that the bridges (11)   join, by the corners, the central area (12) to the corners of the belt area (13).   3. Sensor according to claim 1 or 2, characterized in that wells (6) formed in the layer (1) and the silicon (2) extend between the bridges (11) so as to thermally insulate the central mass of silicon (5) relative to the substrate of silicon (2).   4. Sensor according to any one of the preceding claims, characterized by   the fact that electronic circuits (71, 72) associated with the resistor and the thermocouple   are integrated into the silicon substrate.   5. Sensor according to any one of the preceding claims, characterized by   the fact that bridges (11) carry heating resistors (31).   6. Application of the sensor according to any one of the preceding claims,   characterized in that the sensor is mounted in an electrical protection device so that the polysilicon resistor (3) is coupled to a current sensor (8)