RU2339011C2 - Temperature infrared sensor with reading circuit - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: temperature sensor includes one-pixel microbolometer matrixes, infrared absorbing layer, at least one support arm bearing at least one hanged diode. At least one support arm is used for electric signal transmission. Sensor includes reading circuit with current output connected in each line. And line switch circuit contains connected closed key providing resistance compensation.

EFFECT: increased transformation coefficient.

5 cl, 1 dwg

Description

The invention relates to microelectronics, and in particular to the field of integrated microbolometers. It is used in night vision devices, detection of ignition sources, and in the analysis of heat sources.

Microbolometric uncooled sensors are widely used due to their low cost and high sensitivity of a wide range of received radiation.

Known thermal infrared sensor and a matrix based on it [1], where each sensor contains:

- substrate

- a temperature sensor having electrical characteristics that change in accordance with a change in temperature caused by the absorption of infrared rays,

- heat-insulating support arms supporting and heat-insulating the specified temperature sensor and containing signal lines for reading electrical signals from the above-mentioned temperature sensor,

- an infrared absorption layer in thermal contact with said temperature sensor, where this temperature sensor and said infrared absorption layer overlaps the above thermally insulating support arms when viewed along the direction of infrared rays incident on said infrared absorption layer, and each of said temperature sensors, said heat-insulating support arms and above said infrared absorption layer, is located respectively in different planes, and these planes the spaces are spatially separated from each other so that the corresponding first and second cavities are located between said temperature sensor and said heat-insulating support arms and between these heat-insulating arms and said infrared absorbing layer.

However, in [1], information reading issues, which are an important characteristic of thermal infrared sensors, are not considered.

The closest technical solution is a matrix of uncooled infrared sensors of low cost based on the CMOS process [2], including:

matrix of single-pixel microbolometers, where each of the microbolometers contains at least one diode,

infrared absorption layer

at least one of the supporting arms for supporting at least one suspended diode, where at least one of the supporting arms serves to transmit electrical signals to at least one diode using an interconnect layer,

- a seamlessly integrated readout circuit manufactured using the standard CMOS process, including a row and column of electronic switches that allow for unique addressing of each pixel to control the voltage of the connected diode in each pixel and extracts information about the absorbed heat from the voltage of the connected diode of each pixel.

However, the technical solutions used in the prototype have drawbacks: the reading circuit shown in the description and protected by claims 13 and 14 of the claims of the prototype [2] uses a voltage output, the feature of which (in contrast to the current output circuit) there is an insufficient level of the output signal compared to the current output, which can be loaded at a sufficiently high resistance to obtain a high output signal level, as well as combine the outputs of several columns of the matrix, which allows us to simplify the scheme of columns OK.

The objective of the present invention is to achieve a technical result, which consists in improving the quality and reducing the cost of manufacturing thermal infrared sensors by choosing a different readout circuit (with current output) used in a thermal infrared sensor that provides a higher conversion coefficient that does not require switching small output signals, as well as an easier-to-fabricate temperature sensor corresponding to each pixel on a semiconductor substrate having a pn diode biased in forward direction.

To achieve the specified technical result in a matrix of uncooled infrared sensors of low cost based on the CMOS process [2], including:

matrix of single-pixel microbolometers, where each of the microbolometers contains at least one diode,

infrared absorption layer

at least one reference arm for supporting at least one suspended diode, while at least one reference arm serves to transmit electrical signals to at least one diode using an interconnect layer,

add elements that are the hallmarks of the proposed device:

- the sensor includes a readout circuit with current output that is built into each line, while the elements that form the readout currents of the lines are transistors corresponding to the columns of the matrix, the common line buses connecting the emitters of the transistors consist of segments of the same length, the choice of line is provided when you turn on channel of the current switch, and a closed key is included in the circuit of the string switch for complete compensation of resistances.

The invention is illustrated in the drawing, which shows the reading circuit.

The element forming the currents for reading the rows Jcl - Jcn are the transistors Tl - Tn corresponding to the columns of the matrix. The column is selected by switching on the channel of the current switch SCq, which connects the current source J1 to the corresponding column of TD diodes. The line is selected by turning on the channel of the current switch SLp, which connects the TDqp diode to the lower potential of the circuit. Thus, for the selected element of column q and row p, the “current mirror” circuit from the current source J1, transistor diode TDpq, and transistor Tq is active. All other elements and circuits are inactive and no current flows through them. In the current mirror circuit, provided that the transistors TDqp and Tq are identical and their temperatures are the same, the collector current Jcq of the transistor Tq is equal in magnitude to the source current J1. The currents of sources J1 and J2 in the circuit are equal, since both sources are completely identical and a high degree of equality of currents in them is ensured by integrated manufacturing technology. The total length of the switched lines for the currents J1 and Jcq will remain the same for any selected pixel, since the common bus connecting the emitters of the transistors Tl - Tn has the same length and geometry as the common line bus of the transistors TD. Resistors Re equal to the total resistance of the suspension beams of transistors TD are also included in the emitters of transistors Tl - Tn. Common line buses connecting transistor emitters consist of segments of the same length with resistance R1. The common busbars of the columns connecting the base of the transistors coincide in length and geometry with the lines of key connections SL0 - SLn and consist of segments with the same resistance value Rc. The same for any choice of column and row is the total resistance of the keys Rs. To completely compensate for the resistances, the constantly switched key SL0 is included in the row switch circuit, and the bus section connecting the key SL0 to the common GND power point consists of segments of resistances Rc and in total has a resistance equal to the resistance of the column buses. Thus, the impedances on the current lines J1 and Jcq are the same at any turn-on and the corresponding voltage drops are compensated for them. Therefore, when the transistors TDqp and Tq have the same temperature, the output current Jout of the “current mirror” is completely compensated by the source current J2 and there is no current dJ at the output of the circuit. The incident infrared radiation creates a temperature difference on the transistor TDqp relative to the transistor Tq, since the transistor TDqp, unlike or Tq, is not directly located on the substrate, but is supported on the supporting beams with low thermal conductivity and is heated by the radiation incident on it by dT. This temperature difference dT causes a difference current at the output of the circuit, of the order of dJ = 0.1 · dT · J (1 / K).

The advantages of this scheme

1. High roundness of circuit conversion - at a load resistance of 50 kOhm and a current of 20 μA, it reaches 1 V / K.

2. Low sensitivity to supply voltage and ambient temperature, which is ensured by the identical geometry and modes of all transistors.

3. Lack of output voltage switch on semiconductor radiation receivers. For switching columns and rows, only current switches are used, the requirements for which are much lower than for the voltage switch of small signals.

4. The structure of the circuit with compensation for the voltage drop across the lines can significantly reduce the requirements for the busbar resistance of columns and rows of the matrix, make them narrower and thereby increase the effective area of semiconductor radiation receivers.

5. The small voltage spread across the sensitive elements of the radiation receivers is determined only by the identity of the receivers themselves, since they are all powered by the same source.

6. Low consumption of the circuit, equal to the consumption of only two current sources.

Patent studies have shown that the set of features of the invention is new, which proves the novelty of the claimed device.

In addition, patent studies have shown that there is no data in the literature showing the influence of the distinguishing features of the claimed invention on the achievement of a technical result, which confirms the "inventive step" of the proposed device.

This set of distinctive features allows to achieve the named technical result.

Literature

1. US patent No. 7005644.

2. Patent Int. Cl. WO / 2005/098380 (PCT / EPO05 / 051529).

Claims (5)

1. Thermal infrared sensor with a readout circuit, including a matrix of single-pixel microbolometers, where each of the microbolometers contains at least one diode, an infrared absorbing layer, at least one reference arm to support at least one suspended diode, while at least one reference arm is used to transmit electrical signals to at least one diode using an interconnect layer, characterized in that the sensor includes a current-sensing readout circuit embedded in each the line, while the elements that form the reading currents of the lines are transistors corresponding to the columns of the matrix, the common line buses connecting the emitters of the transistors consist of segments of the same length, the line selection is provided when the current switch channel is turned on, and it is included in the line switch circuit for full compensation resistances closed key. 2. Thermal infrared sensor with a readout circuit according to claim 1, which contains a crystal on which all the elements of the readout circuit are located. 3. The thermal infrared sensor with a readout circuit according to claim 2, in which the identical sizes, arrangement and orientation of the readout circuit elements ensure their complete uniformity in the manufacture by integral technology methods. 4. The thermal infrared sensor with a readout circuit according to claim 1, in which, in the readout circuit, the total length of the switched lines for the currents and their resistance are the same for any selected pixel. 5. The thermal infrared sensor with a readout circuit according to claim 1, wherein in the readout circuit, when the column and row are selected, the same impedance of the switch lines is provided.

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