CN114639768B - Atomic layer thermopile heat flow sensor and batch preparation method thereof - Google Patents

Abstract

The invention belongs to the field of heat flow sensors, in particular to an atomic layer thermopile heat flow sensor and a batch preparation method thereof. The atomic layer thermopile heat flow sensor proposed by the present invention has good stability; the design idea of batch preparation technology is simple and easy, and it can be mass-produced at one time on the inclined single crystal substrate with a large area of more than one inch through special graphic structure design Thousands of small ALTP heat flow sensors are easy to industrialized mass production, greatly improving work efficiency and reducing costs. At the same time, array samples containing 2m, nm and other functional layer lines can be cut out, which is convenient for testing with different numbers of samples according to different requirements, and can effectively meet the application scenarios of large thermal flow field measurement requirements, and facilitate the formation of integration The sensor chip module gives full play to the characteristics of the microsystem that can be standardized and mass-produced, which is in line with the development law of circuits in today's era.

Description

A kind of atomic layer thermopile heat flow sensor and batch preparation method thereof

technical field

The invention belongs to the field of heat flow sensors, and specifically relates to an atomic layer thermopile heat flow sensor and a batch preparation method thereof, which realizes the controllable production of batch arrays of heat flow sensors, mature and controllable technology, and specifically relates to thin film technology and microfabrication technology.

Background technique

The traditional thin-film thermopile heat flow sensor uses the principle of the longitudinal thermopile effect, and requires at least two materials with large differences in Seebeck coefficients, which greatly increases the cost of the thin-film heat flow sensor. The atomic layer thermopile (ALTP) heat flow sensor is based on the transverse Seebeck effect, and its sensitive element only needs one ALTP material. When the ALTP material grows obliquely, the film will form an atomic-level thermocouple due to anisotropy, and the entire film structure is like a series thermocouple with a line density as high as 10 ⁶ /cm. Its structure is shown in Figure 1, so ALTP The heat flow sensor is very advantageous in sensitivity, and can also greatly reduce the production cost of the device.

At the same time, the ALTP heat flow sensor has the characteristics of fast response. Because its heat diffusion and heat absorption occur on the nanoscale film thickness, the heat capacity will be very small, and the generation of the signal does not need to establish a heat balance, so the response speed is more advantageous than other types of heat flow sensors.

In some application scenarios, small heat flow needs to be tested or the resolution of heat flow is very high, so the device needs to have a high sensitivity coefficient. Often in these scenarios, higher spatial resolution is required at the same time, so there is a great limitation on the size of the device. At the same time, more and more attention is being paid to the testing and analysis of high-frequency pulsating heat flow in wind tunnel experiments at home and abroad, among which the ALTP heat flow sensor is mainly used for testing. In this type of test, the miniaturized ALTP heat flow sensor will bring The advantages of small measuring points and little interference to the thermal flow field have great advantages in this type of experiment.

And in the application scenario of measuring large heat flow field, the industry often adopts the physical amplification mode of thermopile line superposition structure to improve the sensitivity of the device; and because there is no good solution at present, the ALTP heat flow sensor of the corresponding size is customized. However, this situation is not conducive to maintaining the miniaturization of the device at the same time. Therefore, it is of great significance to study the ALTP heat flow sensor and its batch preparation method, which can not only solve the domestic demand problem, but also improve efficiency and further reduce costs.

Contents of the invention

In view of the above existing problems or deficiencies, the present invention provides an atomic layer thermopile heat flow sensor and its batch preparation method, further optimizes the device structure of the ALTP heat flow sensor, and performs batch production and manufacturing at the same time in the face of the measurement of a large heat flow field to meet demand.

An atomic layer thermopile heat flow sensor includes a functional layer, a metal layer, a single crystal substrate and lead wires.

The single crystal substrate has an oblique orientation, and the functional layer is an atomic layer thermopile thin film line covering the single crystal substrate parallel to the oblique direction of the single crystal substrate; the metal layer is divided into metal layer lines and metal layer electrodes according to the graphic structure, and the metal layer Layer lines connect the atomic layer thermopile film lines of the functional layer end to end in sequence; the metal layer electrodes are the two outermost electrodes of the functional layer, and are connected with lead wires respectively, which is convenient for connection testing.

The metal layer includes a transition layer and a conductive layer. The transition layer is deposited on the single crystal substrate, and the conductive layer is deposited on the transition layer. The two belong to an upper and lower layered relationship, which is used to enhance the adhesion of the conductive layer on the substrate and improve the device performance. stability.

Further, the thickness of the functional layer is 240-260 nm.

Further, the transition layer is titanium, the conductive layer is gold, the line width of the metal layer is 10 μm, and the length is 800 μm, and the electrode width of the metal layer is 400 μm, and the length is 600 μm.

A batch preparation method of an atomic layer thermopile heat flow sensor, as shown in Figure 3, comprises the following steps:

Step 1. Epitaxially grow an ALTP functional layer thin film on a large-area monocrystalline substrate with an oblique orientation of more than one inch by metal-organic chemical vapor deposition.

Step 2, the first positive photolithography:

The functional layer thin film is prepared as a functional layer line parallel to the inclination direction of the single crystal substrate. As shown in FIG. 4 , the dark part is the functional layer lines, and the light part is the bare drain single crystal substrate after the redundant part of the functional layer pattern is removed.

Taking the direction parallel to the functional layer lines (that is, the inclination direction of the single crystal substrate) as the longitudinal direction, and taking the space between two adjacent metal electrodes as a column group, a total of n column groups (n≥40) functional layer line groups are prepared, wherein each column The group includes m (m≥20) parallel and equally spaced functional layer lines, and the functional layer lines are all over the single crystal substrate.

Step 3, the second negative photolithography:

On the single crystal substrate obtained in step 2, the transition layer and the conductive layer of the metal layer are deposited in sequence, and then the metal layer is prepared into a metal layer line and a metal layer electrode through a lift-off process; the metal layer line connects two adjacent functional layer lines end to end , the metal layer electrodes are at both ends of the ALTP heat flow sensor of each preset size structure. Some device schematic diagrams are shown in Figure 5 and Figure 6.

Step 4, cutting each ALTP heat flow sensor on the single crystal substrate obtained in Step 3. The cutting line is the longitudinal centerline of each metal layer electrode.

Step 5, lead wires on the metal layer electrodes of the cut ALTP heat flow sensor devices, as shown in FIG. 7 , which is convenient for subsequent testing.

Further, the width of the lines of the functional layer is 10 μm, the distance between groups of lines is 400 μm, and the distance between lines within a group is 30 μm. The line structure of each functional layer is the same. Since the single crystal substrate is circular, there is only a difference in the length of the functional layer lines covering the entire single crystal substrate along the surface.

Further, with the direction perpendicular to the line of the functional layer as the horizontal direction, the metal layer is also divided into N row groups (N≥40) in the lateral direction, and a cutting interval (such as 400 μm) is set between each row group, which is reserved for subsequent cutting and Clearance of packaged devices. The metal layer of each row group includes n column groups of metal layer lines and corresponding metal layer electrodes, which are all over the single crystal substrate.

Further, when cutting, line array samples of double devices or n devices containing 2m~nm functional layer lines can be cut according to requirements, and then all metal layer electrodes of the line array samples can be wired, and then used according to requirements. Samples with different numbers of devices were tested.

The batch preparation method of the present invention first satisfies batch production on a large-area single-crystal substrate of more than one inch, and improves efficiency. At the same time, there is a cascade of functional layer lines inside a single ALTP heat flow sensor, which can also amplify the output accordingly. Its structure is shown in Figure 2. The size of the entire device is 1mm ² . Its miniaturization and high sensitivity all meet the test requirements for low heat flow in supersonic wind tunnel tests.

The present invention adopts a special graphic structure design, utilizes thin film deposition technology, grows functional layers and metal layers on obliquely oriented single crystal substrates, and then utilizes microfabrication technology to prepare ALTP heat flow sensors with special graphic structures, which is easy to industrialize in large quantities Production, greatly improving work efficiency and reducing costs. After the sensor is prepared, to a certain extent, it solves the test and test requirements of the hypersonic wind tunnel test in China, and brings the advantages of small measuring points, little interference to the heat flow field, and does not reduce the sensitivity of the heat flow sensor, and the response speed There are also certain advantages. At the same time, array samples containing 2m, nm and other functional layer lines can be cut out, so that it is convenient to select different numbers of samples for testing according to different needs during testing.

To sum up, the atomic layer thermopile heat flow sensor proposed by the present invention has good stability, and the design idea of batch production technology is simple and feasible. It can not only mass produce ALTP heat flow sensor devices, but also combine unit structures according to specific needs The application scenario of measurement requirements for large thermal flow field is in line with the development law of circuits in today's era.

Description of drawings

Figure 1 is a diagram of the orientation relationship of the structure of an ALTP film grown obliquely on a single crystal substrate.

Fig. 2 is a schematic diagram of the principle of batch longitudinal sample structure.

Fig. 3 is a process flow diagram of the present invention.

Fig. 4 is a line structure diagram of the functional layer of the present invention.

Fig. 5 is an example diagram of the metal conductive layer of the embodiment.

Fig. 6 is a structural diagram of batched samples of the embodiment.

Fig. 7 is a schematic diagram of sample leads of the embodiment.

Figure 8 is the XRD test pattern of the example sample, Figure 8a is the 2θ-ω spectrum, Figure 8b is the ω scan spectrum, and Figure 8c is the in-plane ψ scan spectrum.

Fig. 9 is a graph showing the heat flow test results of the device of the embodiment. Fig. 9a is a single-device laser test curve, and Fig. 9b is a double-device laser test curve.

Fig. 10 is a top view of the structure of a batched single crystal substrate.

Detailed ways

The technical scheme of the present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Example:

Step 1. Epitaxial growth of YBCO film by DC magnetron sputtering.

Clean the two-inch inclined LAO single crystal substrate, put the substrate into the deposition chamber after cleaning, and start the deposition experiment after vacuuming to 2×10 ^-3 Pa. Firstly adjust the heating temperature to 830°C, oxygen partial pressure 10Pa, argon partial pressure 20Pa, sputtering current 0.5A, deposit for 5 hours, and the thickness is 250nm at this rate. After the deposition is completed, turn off the sputtering and lower the temperature to 450°C, fill the chamber with oxygen to a pressure of 1×10 ⁵ Pa, and anneal for 45 minutes.

Step 2, patterning the YBCO thin film by first photolithography.

Firstly, the positive photoresist is coated, and the sample is placed on the homogenizer, and the rotation speed and time are set so that the photoresist is evenly distributed on the two-inch substrate. Then put the sheet with photoresist on the heating table for baking, that is, bake at 100°C for 65s to improve the adhesion between the sample and the photoresist. Perform contact exposure for 3.2s. The sample was immersed in the developer solution for 20s to wash away the exposed part of the photoresist, and then the sample was cleaned.

Step 3, using an ion beam etching machine to etch the sample, so that the patterns on the surface that are not protected by photoresist are removed. The etching rate is about 10nm/min, and the etching experiment cannot be carried out continuously for a long time, otherwise the photoresist will be easily denatured if the temperature is too high, and the subsequent removal of the adhesive is extremely difficult. After the etching is completed, the excess photoresist is washed away with acetone to form YBCO lines that evenly cover the entire single crystal substrate.

Step 4, using the second photolithography process and DC magnetron sputtering to realize the pattern preparation of the metal layer.

First, spin-coat the negative photoresist, the time and rotation speed are the same as those of the positive photoresist, run at 1000r/s for 10s, and run at 3000r/s for 30s, so that the photoresist is evenly spin-coated on the surface of the film; place the substrate Pre-bake on a heating stage at 100°C for 65s to improve the adhesion between the photoresist and the sample surface. Use a mask plate for contact exposure for 3.2s, then place the substrate on a heating table at 120°C and bake for 90s, then pan-exposure for 45s, immerse the sample in the developer solution, and gently shake to dissolve the unexposed part of the photoresist, and Wash and dry.

Put the sample into the cavity of the DC magnetron sputtering gold plating equipment, vacuum it to below 7×10 ^-4 Pa, and start the sputtering experiment. First, argon gas is filled to 1.2×10 ^-2 Pa, and the deposition of titanium transition layer is started. The titanium target sputtering current was set at 80mA and the rate was 10nm/min. Then conduct gold conductive layer deposition, gold target sputtering current is set to 100mA, rate is 60nm/min. Since the film thickness is 250nm, it only needs to deposit titanium for 2 minutes and deposit gold for 4 minutes. Finally, use acetone to remove the remaining photoresist on the surface of the substrate.

Step 5. Prepare thousands of small ALTP heat flow sensor devices in batches on a two-inch sample, which needs to be cut with a dicing machine. Firstly, coat the prepared sample with a layer of protective glue to prevent dust from polluting the surface of the sample when slicing. Then stick the back of the sample on the blue film, put it into the dicing machine, install a soft knife with a width of 200 μm, and set the cutting program for cutting.

Step 6. Wire the cut small devices to facilitate subsequent external test connections.

The prepared sample was subjected to laser induced voltage test and XRD analysis, the results are as follows:

Carry out XRD test to the sample, its result is shown in Figure 8: Figure a is the 2θ-ω spectrum of YBCO, and its (005) peak is near 38.6 °; Figure b is the ω scanning figure of YBCO (005) crystal plane, peak position At 31.6°, it can be seen that YBCO grows along the direction of the 12.3° inclination of the substrate normal; c is the ψ scanning spectrum, and the in-plane half maximum width Δψ = 1.02, indicating that the crystal quality of the film is good.

The laser induced voltage test was performed on the sample device of this embodiment, the laser energy was 0.4J, and the pulse width was 28ns. Figure 9a is the test curve of a single-device sample, and the heat flow potential output is 25V; Figure 9b is the heat flow test curve of a double-device sample, with an output potential of 50V, and the response time of both devices is at the level of hundreds of nanoseconds. At the same time, the potential output of the double-device sample is about twice that of the single-device sample.

It can be seen from the above examples that the present invention grows a functional layer and a metal layer on an obliquely oriented single crystal substrate through a special patterned structure design on an inclined single crystal substrate with a large area of more than one inch, and then Using micro-processing technology, thousands of small ALTP heat flow sensors can be mass-produced at one time, which is easy to industrialized mass production, greatly improving work efficiency and reducing costs. At the same time, array samples containing 2m, nm and other functional layer lines can be cut out, which is convenient for testing with different numbers of samples according to different requirements, and can effectively meet the application scenarios of large thermal flow field measurement requirements, and facilitate the formation of integration The sensor chip module gives full play to the characteristics of the microsystem that can be standardized and mass-produced, which is in line with the development law of circuits in today's era.

Claims (6)

1. An atomic layer thermopile heat flow sensor, comprising a functional layer, a metal layer, a single crystal substrate and a lead, is characterized in that; The single crystal substrate has an oblique orientation, and the functional layer is an atomic layer thermopile thin film line covering the single crystal substrate parallel to the oblique direction of the single crystal substrate; the metal layer is divided into metal layer lines and metal layer electrodes according to the graphic structure, and the metal layer The layer lines connect the atomic layer thermopile thin film lines of the functional layer from end to end in sequence; the metal layer electrodes are the two outermost electrodes of the functional layer, and are respectively connected with lead wires; The metal layer includes a transition layer and a conductive layer, the transition layer is deposited on the single crystal substrate, the conductive layer is deposited on the transition layer, and both belong to the upper and lower stacking relationship, and are used to enhance the adhesion of the conductive layer on the substrate; The batch preparation method of the atomic layer thermopile heat flow sensor comprises the following steps: Step 1. Epitaxial growth of a functional layer thin film on a large-area monocrystalline substrate with an oblique orientation of more than one inch; Step 2, the first positive photolithography: preparing the functional layer thin film into functional layer lines parallel to the inclination direction of the single crystal substrate; With the direction parallel to the functional layer lines as the longitudinal direction, two adjacent metal electrodes form a column group, and a total of n column groups of functional layer line groups are prepared, n≥40; each column group contains m equally spaced parallel functional layers Lines, m≥20, the functional layer lines cover the entire single crystal substrate; the functional layer line structure of each column group is the same, since the single crystal substrate is circular, there is only a difference in length between the functional layer lines covering the entire single crystal substrate; Step 3, the second negative photolithography: On the single crystal substrate obtained in step 2, the transition layer and the conductive layer of the metal layer are deposited in sequence, and then the metal layer is prepared into a metal layer line and a metal layer electrode through a lift-off process; the metal layer line connects two adjacent functional layer lines end to end , the metal layer electrodes are at both ends of the ALTP heat flow sensor of each preset size structure; In the step 3, the direction perpendicular to the line of the functional layer is taken as the horizontal direction, and the metal layer is also divided into N row groups in the lateral direction, N≥40, and a cutting distance is set between each row group, which is reserved for subsequent cutting and packaging of devices. Gap; wherein the metal layer of each row group includes n column groups of metal layer lines and corresponding metal layer electrodes, covering the entire single crystal substrate; Step 4, cutting each ALTP heat flow sensor on the single crystal substrate obtained in step 3, the cutting line is the longitudinal centerline of each metal layer electrode; Step 5, lead wires on the metal layer electrodes of each cut ALTP heat flow sensing device. 2 . The atomic layer thermopile heat flow sensor according to claim 1 , wherein the thickness of the functional layer is 240-260 nm. 3. The atomic layer thermopile heat flow sensor according to claim 1, wherein the transition layer is titanium, and the conductive layer is gold. 4. The atomic layer thermopile heat flow sensor according to claim 1, characterized in that: the width of the functional layer lines is 10 μm, the distance between groups of lines is 400 μm, and the distance between lines within a group is 30 μm. 5. The atomic layer thermopile heat flow sensor according to claim 1, characterized in that: the cutting distance between each row group is 400 μm, the line width of the metal layer is 10 μm, the length is 800 μm, the electrode width of the metal layer is 400 μm, the length is 600 μm. 6. The atomic layer thermopile heat flow sensor as claimed in claim 1, characterized in that: when cutting, the line array samples of double devices or n devices containing 2m-nm functional layer lines are cut according to the requirements, and then the line array All metal layer electrodes of the sample are lead wires.

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