EA043242B1 - THIN-FILM PLATINUM THERMISTOR ON A GLASS SUBSTRATE AND METHOD FOR ITS MANUFACTURE - Google Patents

Description

The invention relates to instrumentation, namely to thin-film thermistors and methods for their manufacture. Such thin-film thermistors are designed for discrete level meters and can be used to control the level and mass flow of fuel components during filling, consumption and storage in the chemical, space and other industries.

The prototype of the claimed inventions is the construction of a thin-film thermistor according to Fig. 4, given in the applicant's patent RU 2506543 C1 dated February 10, 2014, IPC G01F23 / 00, G01K7 / 16, called Sensor for controlling discrete levels of liquid with the function of measuring temperature and controlling the mass flow of a liquid medium [1]. In [1] (Fig. 4) a thin-film platinum resistor is presented on a thin heat-insulating substrate (hereinafter referred to as the thermistor) of a rectangular shape with a width of about 1 mm, on which a meander-shaped film resistor is placed in the center (hereinafter referred to as the meander of the thermistor) of a point design , and along the edges of the long side of the rectangular substrate there are contact pads, which are connected to the thermistor meander in the form of wedges, and rectangles (which are not indicated and not disclosed in [1]) are applied to the sections of the substrate free from the thermistor meander and contact pads. The thermistor meander is made in a point design on an area of not more than 0.3x0.3 mm and a thickness of not more than 0.15 microns. The remaining parameters of the thermistor [1] were not disclosed and were the know-how of the applicant, because in the invention - the prototype - it is not the thin-film thermistor itself that is claimed, but a sensor for controlling discrete levels of liquid with the function of measuring temperature and controlling the mass flow of the liquid medium in the assembly.

The disadvantage of the prototype [1] is that the thin-film thermistor included in its composition cannot be manufactured without disclosure of the Applicant's Know-How, including without specifying the materials of its components, as well as without specifying specific dimensions, ranges of their change and technological modes.

The method for manufacturing thin-film platinum thermistors on glass substrates according to the prototype device [1], as well as other known similar devices, consists in sequential deposition of an adhesive sublayer and the main layer (platinum resistive layer) on a thin dielectric substrate, photolithography and etching to form thin-film resistors.

The disadvantage of this method of manufacturing thin-film platinum thermistors on glass substrates is that the etching of platinum causes certain difficulties and for its etching it is necessary to use other methods, for example, long-term etching in strong etchants (aqua regia) or the use of ion-plasma etching, which requires special technological equipment and additional production costs. The use of reverse photolithography technology with etching of the sacrificial layer of photoresist can significantly simplify the method of manufacturing thin-film platinum thermistors on a glass substrate, however, their quality is low due to the formation of the so-called veil - photoresistor residues, as well as the resulting uneven edges (boundaries) of the platinum film.

The disadvantages of the device and the method of its manufacture according to [1] pose the problem of improving the manufacturability of the design, i.e. optimization of its dimensions and materials used, as well as simplification of the manufacturing technology of the device by improving the technology of reverse explosive photolithography of the sacrificial layer and the main platinum layer to improve the accuracy of obtaining geometric dimensions.

The essence of the claimed device is that a thin-film platinum thermistor on a glass substrate (hereinafter referred to as the thermistor) is rectangular in shape, on which a meander-shaped film resistor is placed in the center (hereinafter referred to as the meander of the thermistor), along the edges of the long side of the rectangular substrate are located (there are ) contact pads, which are connected to the thermistor meander in the form of wedges, the thermistor meander is made in a point design, rectangles are applied to the areas of the substrate free from the thermistor meander and contact pads. In this case, the dimensions of the thermistor rectangles are commensurate with the width of the gaps between the thermistor meander strips, and the distances between them are equal to the gaps between the thermistor meander strips. The substrate is made of thin heat-insulating cover glass 0.10...0.19 mm thick, 4...6 mm long, 0.6...1.2 mm wide. The meander of the thermistor occupies an area (0.20x0.20mm) ... (0.4x0.4 mm). The thermistor meander, its contact pads and rectangles are made of a 0.15...0.25 µm thick platinum layer, and a 0.01...0.02 µm thick titanium layer is used as an adhesive sublayer between the glass substrate and the platinum layer.

The essence of the claimed method lies in the fact that the method of manufacturing thin-film platinum thermistors on a glass substrate (in the form of a thin dielectric glass plate from cover glass with a thickness of 0.10 ... 0.19 mm) consists in sequentially applying a sacrificial layer (photoresist ), carrying out photo exposure, developing the pattern of the sacrificial layer of the photoresist, deposition of the adhesive sublayer and the main layer - platinum - and further carrying out reverse photolithography with the removal of the sacrificial layer (photoresist) with films of the adhesive sublayer and the main layer - platinum, and allows you to form thin-film thermo- 1 043242 resistors (leads to the formation of thin-film thermistors). In this case, the sacrificial layer is formed from aluminum by successive deposition in a vacuum on a cover glass plate of a sacrificial layer of aluminum with a thickness of 0.5...1 μm at a temperature of 150...200°C and applying a photoresist layer. Next, photo-exposure of the photoresist is carried out with the formation of a pattern on the aluminum layer, etching of the sacrificial aluminum layer and washing off the remains of the photoresist (from the surface of the sacrificial aluminum layer). Then, at a temperature of 150 ... 200 ° C, successive deposition is carried out on a substrate with a pattern of a sacrificial aluminum layer of an adhesive sublayer of titanium with a thickness of 0.01 ... 0.02 μm and the main layer - platinum - with a thickness of 0.15 ... 0 .25 µm. Reverse explosive photolithography of the sacrificial aluminum layer is carried out with films of the adhesive titanium sublayer and the main layer - platinum deposited on it. Annealing is carried out in vacuum at a temperature of 150...250°C for 20...50 min and the substrate is divided (cut) into separate thermistors, each of which has their contact pads covered with a solder layer and each thermistor is electrically trained.

The technical result of the device and the method for its implementation is to increase manufacturability and reduce costs in the manufacture of (high-quality) point-type thermistors, in which the accuracy of their geometric dimensions is increased.

An increase in manufacturability and a reduction in costs in the manufacture of thermistors is achieved by the fact that strong concentrated etchants, such as aqua regia, are not required for etching platinum, since only the aluminum layer is quickly chemically etched, with the removal of the adhesive sublayer of titanium and the main layer of platinum.

The use of rectangles located on free areas from the meander and contact pads made of platinum, where the dimensions of the thermistor rectangles are commensurate with the width of the gaps between the thermistor meander strips, and the distances between them are equal to the gaps between the thermistor meander strips, allows etching the sacrificial aluminum layer (with the removal of titanium and platinum films ) on the entire surface of the substrate simultaneously, i.e. removal of all etching areas in a shorter and equal time, which significantly increases the manufacturability of production and reduces its costs. In this case (with short, reduced etching times), the edges of the platinum layers deposited on the substrate are more even, which additionally improves the quality of the resulting thermistors. The application of the main layer - platinum - greater thickness of 0.15...0.25 microns than the prototype (not more than 0.15 microns), leads to a significant reduction in the influence of thickness errors on the resistance of the thermistor. In turn, an increase in the thickness of the main layer - platinum (thermistor) - leads to the possibility of increasing the heating current of the meander of the thermistor, reducing its overall dimensions, as well as increasing sensitivity. All this (reducing the influence of the thickness error on the resistance of the thermistor, increasing the heating current of the thermistor meander, reducing its overall dimensions and increasing the sensitivity) additionally ultimately also improves the manufacturability of the production of thermistors (the claimed device and method) leads to a decrease in the cost of thermistors.

The essence of the claimed device and method of its manufacture is illustrated by graphic materials.

In FIG. 1 is a top view of a thin film platinum thermistor on a glass substrate.

In FIG. 2 shows the structure of a film thermistor in a cross-sectional section (contact pad).

In FIG. 3 - part of the sensor board with a thin-film platinum thermistor soldered to it on a glass substrate.

In FIG. 4 shows a sensor (for a sensor) with the claimed thermistor soldered to the board.

In FIG. Figure 5 shows the sequence of operations for a standard technology for manufacturing thin film thermistors, in which a positive photoresist is used for the mask, where

a) - a substrate with a layer of sacrificial photoresist applied;

b) - a mask of sacrificial photoresist after development with a pattern of sacrificial photoresist;

c) - deposited on a substrate with a layer of sacrificial photoresist (with a pattern) of an adhesive sublayer and a base layer (platinum);

d) - the process of explosive etching (removal) of the sacrificial photoresist (pattern) with layers of the adhesive sublayer and the main layer (platinum);

e) - a substrate with an applied adhesive sublayer and a main layer (platinum).

In FIG. 6 shows the sequence of operations of the claimed technology for manufacturing thin-film platinum thermistors using a sacrificial aluminum mask, where

a) - a substrate with applied layers of sacrificial aluminum and photoresist;

b) - a mask (drawing) made of sacrificial aluminum after developing the photoresist, etching the sacrificial aluminum layer and removing the remains of the photoresist;

c) - applied to the substrate with a layer (pattern) of sacrificial aluminum layers of the adhesive sublayer and the main layer (platinum);

d) - the process of explosive etching of a pattern of sacrificial aluminum with layers of adhesive underlay

- 2 043242 layers and base layer (platinum);

e) - a substrate with an applied adhesive sublayer and a main layer (platinum).

In FIG. 7 - sensor (for the sensor) with a thin-film platinum thermistor soldered to the board with three point-type resistors located on the same glass substrate with contact pads located on opposite sides of the long side of the glass substrate (on its short sides).

In FIG. 8 - sensor (for the sensor) with a thin-film platinum thermistor soldered to the board with three point-type resistors located on the same glass substrate with contact pads located on one short side of the glass substrate.

The claimed device - thermistor - is made on a glass substrate (1) of a rectangular shape, on one side of which is applied from a platinum film: in the center of the substrate (1) a meander (2) of the thermistor, along the edges of the long side of the rectangular substrate (1) (on its short sides ) there are contact pads (3), which are connected to the meander (2) of the thermistor in the form of wedges. The meander (2) of the thermistor is made in a dot design, rectangles (4) are applied to the areas of the substrate free from the meander (2) of the thermistor and contact pads (3). In this case, the dimensions of the thermistor rectangles are commensurate with the width of the gaps between the meander strips (2) of the thermistor, and the distances between them are equal to the gaps between the meander strips (2) of the thermistor. The substrate (1) is made of thin heat-insulating cover glass 0.10...0.19 mm thick, 4...6 mm long, 0.6...1.2 mm wide. The meander (2) of the thermistor occupies an area (0.20x0.20 mm) ... (0.4x0.4 mm). Meander (2) of the thermistor, its contact pads (3) and rectangles (4) are made of a layer of platinum film (5) 0.15...0.25 µm thick, and as a sublayer between the glass substrate (1) and the layer platinum (5) an adhesive layer of titanium (6) with a thickness of 0.01 ... 0.02 microns is applied. In FIG. 3 and 4, the thermistor on a glass substrate (1) is shown soldered to the printed tracks of the sensor board (7) with its solder-coated (for example, tinned) pads (3).

A well-known method for manufacturing thin-film platinum thermistors on glass substrates (according to the restrictive features of the formula) is schematically presented in Fig. 5. It should be noted that according to the well-known production technology, initially many thermistor topologies are applied to one substrate, and at the end of the process of forming a plurality of thermistors on one substrate, the substrate is divided (cut) along the boundaries of each topology and a plurality of thermistors are obtained. The method consists in successively applying a sacrificial layer (photoresist) (8) (Fig. 5a) on a thin dielectric substrate (1), carrying out its photo exposure and developing the pattern of the sacrificial photoresist layer (8) (Fig. 5b)), spraying an adhesive sublayer ( 6) and the main layer - platinum (5) (Fig. 5c)) - and further reverse photolithography with the removal of the sacrificial layer (photoresist) (8) with films of the adhesive sublayer (6) and the main layer - platinum (5) (Fig. 5d)), leading to the formation of thin-film thermistors (Fig. 5e)).

In the claimed method shown in FIG. 6 (according to the restrictive and distinguishing features of the formula), as a thin dielectric substrate, a large glass plate (1) made of cover glass with a thickness of 0.10 ... On the glass plate (1) for each thermistor, its topology includes a meander (2) of the thermistor, contact pads (3), which are connected to the meander (2) of the thermistor in the form of wedges, and also located on the thermistor free from the meander (2) and its contact pads. sites (3) sections of the substrate are rectangles (4), the dimensions of which are strictly regulated. So (according to the distinctive features of the device), the dimensions of the thermistor rectangles are commensurate with the width of the gaps between the meander strips (2) of the thermistor, and the distances between them are equal to the gaps between the meander strips (2) of the thermistor. Compliance with these dimensions allows explosive reverse photolithography of the sacrificial layer in all areas of the thermistor topology for the same time (and a shorter time compared to known methods), which significantly increases the manufacturability of thermistors and improves their quality. The sacrificial layer is formed from aluminum by successive vacuum deposition on a cover glass plate (1) of a sacrificial aluminum layer (9) with a thickness of 0.5..1.0 μm at a temperature of 150...200°C and applying a photoresist layer (8) fig. 6a)). Next, photo-exposure of the photoresist (9) is carried out with the formation of a pattern on the aluminum layer (9), etching of the sacrificial aluminum layer (9) and washing off the remains of the photoresist (8) (Fig. 6b)) from the aluminum layer (9). Then, at a temperature of 150 ... 200 ° C, sequential deposition is carried out on the substrate (1) with a pattern of the sacrificial aluminum layer (9) of the adhesive sublayer of titanium (6) with a thickness of 0.01 ... 0.02 μm and the main layer - platinum (5) - 0.15...0.25 µm thick (Fig. 6c)). Reverse explosive photolithography of the sacrificial aluminum layer (9) is carried out with films of the adhesive sublayer of titanium (6) and the main layer - platinum (5) (Fig. 6d)) applied on it, leading to the formation of thin-film thermistors (Fig. 6d)).

Next, a large glass plate (1) with thermistors formed on it is annealed in vacuum at a temperature of 150...250°C for 20...50 min, after which it (the large glass plate) is separated, for example, by cutting the substrate (1 ) to individual thermistors. For each thermistor obtained after cutting a large glass plate (1), the contact pads (3) are covered with a layer of solder. The solder coating of the contact pads (3) of each thermistor can be carried out on one (large) glass plate before it is separated (cut) into separate thermistors, which further increases the manufacturability of production and reduces its cost.

After that, each thermistor is (individually) electrically trained, for example, through wires soldered to its contact pads (3) or contact tracks of a printed circuit board using Flip-Chip technology, for example, already on the sensor board (Fig. 3 and 4).

The specific execution of the claimed device and method for its implementation, which are implemented and tested by the applicant, is as follows. The substrate is made of a thin heat-insulating cover glass 0.17 mm thick, 5 mm long, and 1 mm wide. The meander of the thermistor occupies an area of 0.25x0.25 mm. The width of the meander resistor strips is 0.04 mm, the gap between the meander strips is also 0.04 mm. The thermistor meander, its contact pads and rectangles are made of a 0.2 µm thick platinum layer, and a 0.015 µm thick titanium layer is used as an adhesive sublayer between the glass substrate and the platinum layer.

The sacrificial layer is formed from aluminum by vacuum deposition on a cover glass plate of a layer of aluminum with a thickness of 0.75 μm at a temperature of 180°C, and then a layer of photoresist is applied. Photo-exposure of the photoresist is carried out with the formation of a pattern on the aluminum layer according to known technology. The sacrificial aluminum layer is etched and the residual photoresist is washed off from the sacrificial aluminum layer. Next, at a temperature of 180°C, successive deposition is carried out on a substrate with a pattern of a sacrificial aluminum layer of an adhesive underlayer of titanium with a thickness of 0.015 μm and the main layer - platinum - with a thickness of 0.2 μm. Reverse explosive photolithography of the sacrificial aluminum layer is carried out with films of the adhesive titanium sublayer and the main layer - platinum deposited on it. Annealing is carried out in vacuum at a temperature of 200°C for 30 min. Cut the substrate (large glass plate) into individual thermistors. For each thermistor, the contact pads are covered with a layer of solder and each thermistor is electrically trained. The sacrificial layer is formed from aluminum by vacuum deposition on a cover glass plate of a layer of aluminum with a thickness of 0.75 μm at a temperature of 180°C, and then a layer of photoresist is applied. Photo-exposure of the photoresist is carried out with the formation of a pattern on the aluminum layer according to known technology. The sacrificial aluminum layer is etched and the residual photoresist is washed off from the sacrificial aluminum layer. Next, at a temperature of 180°C, successive deposition is carried out on a substrate with a pattern of a sacrificial aluminum layer of an adhesive underlayer of titanium with a thickness of 0.015 μm and the main layer - platinum - with a thickness of 0.2 μm. Reverse explosive photolithography of the sacrificial aluminum layer is carried out with films of the adhesive titanium sublayer and the main layer - platinum deposited on it. Annealing is carried out in vacuum at a temperature of 200°C for 30 min. Cut the substrate (large glass plate) into individual thermistors. For each thermistor, the contact pads are covered with a layer of solder and each thermistor is electrically trained.

According to the claimed technical solutions, devices (thermistors) with several film resistors can be manufactured. For example, shown in Fig. 7 and 8 devices of thermistors with combined point-type resistors located on the same glass substrate.

In addition, the contact pads of such thermistors with combined point-type resistors can be located both on opposite sides of the substrate, and on one side of the substrate, as, for example, in the analogue in Fig. 3. Thus, in FIG. 7 shows a thin-film platinum thermistor with three point-type resistors located on the same glass substrate with contact pads located on opposite sides of the long side of the glass substrate (on its short sides). In FIG. 8 shows a thin-film platinum thermistor with three point-type resistors located on the same glass substrate with contact pads located on one short side of the glass substrate. In this case, the thermistors according to Fig. 7 and 8 are soldered using Flip Chip technology to the sensor board for a gas or liquid flow sensor.

Literature.

1. Patent for the invention of the Russian Federation (applicant): RU 2506543 C1 dated 10.02.2014, IPC G01F 23/00, G01K 7/16 under the name Sensor for controlling discrete levels of liquid with the function of measuring temperature and controlling the mass flow rate of a liquid medium - a prototype.

Claims (2)

1. A thin-film platinum thermistor on a rectangular glass substrate, on which a meander-shaped film resistor is placed in the center, contact pads are located along the edges of the long side of the rectangular substrate, which are connected to the thermistor meander in the form of wedges, moreover, on the thermistor and contact pads free from the meander sections of the substrate are marked with rectangles, characterized in that the dimensions of the rectangles of the thermistor - 4 043242 are commensurate with the width of the gaps between the thermistor meander strips, and the distances between them are equal to the gaps between the thermistor meander strips, the substrate is made of thin heat-insulating cover glass 0.10...0.19 mm thick, 4...6 mm long, wide 0.6 ... 1.2 mm, the thermistor meander occupies an area of (0.20x0.20 mm) ... (0.4x0.4 mm), the thermistor meander, its contact pads and rectangles are made of a platinum layer with a thickness of 0, 15...0.25 µm, and a layer of titanium 0.01...0.02 µm thick is used as an adhesive sublayer between the glass substrate and the platinum layer. 2. A method for manufacturing thin-film platinum thermistors on glass substrates, which consists in sequentially applying a sacrificial layer on a thin dielectric substrate, performing photo exposure, developing a pattern of the sacrificial photoresist layer, deposition of the adhesive sublayer and the main layer - platinum - and then carrying out reverse photolithography with the removal of the sacrificial layer from films of the adhesive sublayer and the main layer - platinum, which makes it possible to form thin-film thermistors, characterized in that the sacrificial layer is formed from aluminum by successive vacuum deposition on a cover glass plate of a sacrificial aluminum layer with a thickness of 0.5 ... 1 μm at a temperature of 150 .. .200°C and applying a layer of photoresist, then the photoresist is photoexposed with the formation of a pattern on the aluminum layer, etching of the sacrificial aluminum layer and washing off the remains of the photoresist, after which successive deposition on the substrate with a pattern from the sacrificial layer is carried out at a temperature of 150...200°C aluminum adhesive sublayer of titanium with a thickness of 0.01 ... 0.02 microns and the main layer - platinum - with a thickness of 0.15 ... layer - platinum, annealing is carried out in vacuum at a temperature of 150 ... 250 ° C for 20 ... 50 minutes and the substrate is divided into separate thermistors, each of which has their contact pads covered with a solder layer and each thermistor is electrically trained.