Method for depositing a thermochromic vanadium dioxide layer on a glass substrate
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- FRAUNHOFER GESELLSCHAFT ZUR FORDERUNG DER ANGEWANDTEN FORSCHUNG EV
- Filing Date
- 2024-06-28
- Publication Date
- 2026-06-10
AI Technical Summary
Existing methods struggle to achieve homogeneous and reproducible deposition of thermochrome vanadium dioxide layers on large and band-shaped glass substrates, due to narrow synthesis parameters and high oxygen affinity of vanadium, leading to inconsistent layer quality.
A dynamic reactive process using a magnetic sputtering method with controlled oxygen flow, where a glass substrate is heated and passed through a coating device with a target of vanadium or vanadium oxide, and light radiation is applied to regulate oxygen inflow based on real-time transmission and temperature feedback from multiple sensors, enabling fine adjustment of oxygen flow for homogeneous layer formation.
This approach allows for the deposition of thermochrome vanadium dioxide layers with consistent properties on large-scale glass substrates, ensuring improved homogeneity and reproducibility by using dual control loops for precise oxygen regulation.
Smart Images
Figure EP2024068329_06022025_PF_FP_ABST
Abstract
Description
[0001] Method for depositing a thermochromic vanadium dioxide layer on a glass substrate
[0002] Description
[0003] The invention relates to a method for depositing a thermochromic layer of vanadium dioxide (VO2) on a glass substrate by means of physical vapor deposition.
[0004] Modern buildings, especially those used commercially, often have a high window-to-wall ratio, which can lead to energy losses when heating and / or cooling the rooms compared to buildings with a low window-to-wall ratio. By coating window panes with films, the reflection and transmission of glass can be influenced. This can advantageously change the energy flow through window panes. Such coatings include so-called smart window coatings, in which the optical properties can be actively or passively modified by external stimuli. Layer systems for smart window coatings can include photochromic, electrochromic, or thermochromic thin films.
[0005] Tetragonal / monoclinic vanadium dioxide (VO2) is becoming increasingly important as a coating material for smart window coatings with thermochromic properties. The change in the optical properties of such a thermochromic vanadium dioxide coating occurs through a change in the ambient temperature. At an ambient temperature lower than the so-called transition temperature, the transmission of light in the infrared spectral range through a glass substrate coated with thermochromic vanadium dioxide is relatively high. Above the transition temperature, the transmission decreases significantly. The transition temperature of a thermochromic vanadium dioxide coating is approximately 68 °C.If such a vanadium dioxide layer is doped with a metal, such as tungsten, the transition temperature of the layer can also be shifted to a range of, for example, 18 °C to 25 °C, which makes the effect of a change in transmission interesting, for example in window glass, for saving energy in air conditioning rooms. Various processes are known for producing layers of thermochromic vanadium dioxide. A process for metal deposition followed by annealing is described, for example, in CN 1 1233155 A. In US 2021 / 0223439 A1, however, it is proposed to first apply a solution containing vanadium oxide particles to a substrate and then remove organic material from the solution. The vanadium oxide particles remaining on the substrate are then subjected to a sintering process to form vanadium oxide clusters.
[0006] Furthermore, processes are known that use reactive magnetron sputtering to deposit thermochromic vanadium oxide layers. However, the parameter window for the synthesis of thermochromic vanadium dioxide is very narrow, since vanadium, due to its high affinity for oxygen, can form many different oxide forms that do not exhibit thermochromic properties.
[0007] The decisive roles in the deposition of stoichiometric, thermochromic vanadium dioxide layers are then played by the oxygen flow control and the deposition temperature, which is usually set to over 300 °C.
[0008] In Sihai Chen et al.'s "Characterization of nanostructured VO2 thin films grown by magnetron-controlled sputtering deposition and post-annealing method," a vanadium oxide layer is first reactively deposited using magnetron sputtering. The inflow of the reactive gas oxygen is adjusted to a predetermined flow rate using gas flow meters. The deposited vanadium oxide layer is then heated to a temperature of 200 °C to 250 °C to convert the vanadium oxide into thermochromic vanadium dioxide.
[0009] In D. Kolenaty et al., "Improved performance of thermochromic VO2 / SiO2coatings prepared by low-temperature pulsed reactive magnetron sputtering: Prediction and experimental verification", Journal of Alloys and Compounds, Volume 767, 30 October 2018, Pages 46-51, thermochromic vanadium dioxide coatings are deposited in a reactive deposition process using high-power pulsed magnetron sputtering. A pulsed reactive gas flow controller is used to regulate the oxygen flow rate for the deposition process. A tungsten-doped vanadium target is used in Jin Rezek et al., "Transfer of the sputter technique for deposition of strongly thermochromic VO2-based coatings on ultrathin flexible glass to large-scale roll-to-roll device".Surface and Coatings Technology, Volume 442, 25 July 2022, 128273, used as a starting material for a reactive sputtering process to deposit thermochromic vanadium dioxide with a transition temperature of approximately 22 °C on a ribbon-shaped glass substrate. The oxygen flow into the working chamber is controlled depending on the pressure in the working chamber.
[0010] All of the previously described processes have successfully deposited thermochromic vanadium dioxide under laboratory conditions. However, the desired homogeneity of the layers and reproducibility of the layer deposition on large areas or ribbon-shaped substrates have not yet been achieved.
[0011] The invention is therefore based on the technical problem of creating a process by which the disadvantages of the prior art can be overcome. In particular, the process according to the invention should make it possible to deposit thermochromic vanadium dioxide on large-area and ribbon-shaped glass substrates. The process according to the invention should also be applicable to roll-to-roll processes.
[0012] The solution to the technical problem results from objects having the features of patent claim 1. Further advantageous embodiments of the invention result from the dependent patent claims.
[0013] In the method according to the invention, a thermochromic vanadium dioxide layer is deposited on a glass substrate within a working chamber using magnetron sputtering. The glass substrate is moved past a coating device within the working chamber. The deposition process is thus dynamic and is also designed as a reactive process. For this purpose, the reactive gas oxygen is admitted into the working chamber through at least one inlet. The flow rate of the reactive gas through the at least one inlet into the working chamber can be regulated by means of a valve.
[0014] Before the layer deposition, the glass substrate is first treated with at least one
[0015] The coating is heated by a heating device and then guided past the coating device in a heated state. The coating device comprises at least one target made of vanadium or vanadium oxide and may also contain doping elements, and at least one magnetron with which the target is sputtered.
[0016] Furthermore, in the method according to the invention (viewed with respect to the direction of movement of the glass substrate), at least one lighting device is arranged downstream of the coating device on one side of the glass substrate, said lighting device emitting light radiation that can be detected by the human eye. The lighting device is aligned such that the light radiation penetrates the coated glass substrate. A first sensor is arranged on the other side of the glass substrate, with which a first actual value can be detected, which characterizes the transmission of the light radiation through the coated glass substrate. The detected first actual value for the transmission of the light radiation is forwarded to an evaluation device, where it is compared with a first target value for the transmission of the light radiation, thus producing a first comparison result.Depending on the initial comparison result, the valve then regulates the flow rate of the reactive gas oxygen through the inlet into the working chamber. However, it has been shown that such an initial control loop is only suitable for coarse control of the oxygen flow, and cannot guarantee the achievability of a homogeneous coating quality even for larger coating surfaces because this control loop reacts too slowly. Thus, the coating properties may have already changed before such a change in the coating properties is detected and counteracted accordingly using the light transmission parameter.
[0017] According to the invention, a second control loop is therefore installed. For this purpose, a second sensor is arranged downstream of the coating device, with which a second actual value can be recorded that characterizes the temperature of the coated glass substrate. The recorded second actual value for the temperature of the coated glass substrate is forwarded to the evaluation device, where it is compared with a second target value for the temperature of the coated glass substrate, thus producing a second comparison result. Depending on the second comparison result, the flow rate of the reactive gas oxygen through the at least one inlet into the working chamber is then regulated by means of the valve. It has been shown that using this procedure, a fine adjustment of the oxygen flow into the working chamber can be carried out in such a way that homogeneous coating properties can be achieved even on large-area glass substrates.
[0018] For glass substrates with a thickness of more than 0.2 mm, the measurement accuracy of the second sensor can be increased by supplementing it with the temperature measurement recording of a third sensor, which can be designed as a pyrometer, for example. The third sensor is arranged on the coated side of the glass substrate and records the temperature on the coated side of the glass substrate. If the deposited vanadium dioxide layer has thermochromic properties, then lower temperature values are recorded with the third sensor than with the second sensor. This is because the values recorded with a pyrometer depend not only on the temperature of an object but also on its emissivity. This emissivity, in turn, is strongly influenced by whether a deposited vanadium dioxide layer is thermochromic or not.This fact can be exploited when evaluating the measured values, i.e. when answering the questions whether a deposited layer has thermochomic properties or whether the oxygen flow needs to be regulated accordingly.
[0019] The invention is explained in more detail below using an exemplary embodiment. The figures show:
[0020] Fig. 1 is a schematic representation of a device suitable for carrying out the method according to the invention.
[0021] Fig. 1 schematically shows a device 100 with which the method according to the invention can be carried out. By means of the device 100, a thermochromic vanadium dioxide layer is to be deposited on a glass substrate 101 within a working chamber. The working chamber is not shown in Fig. 1 for reasons of clarity. The flexible glass substrate 101 is initially located on an unwinding roll 102, is unwound from this, guided past a coating device 103 and, after the layer has been deposed, wound onto a take-up roll 104. The direction of movement of the glass substrate 101 is also shown in Fig. 1 with a horizontal arrow. The belt speed can be set, for example, in a range from 0.1 m / min to 1 m / min. In the exemplary embodiment, the glass substrate 101 is flexible. Alternatively, plate-shaped glass substrates can also be used in the method according to the invention.In the process according to the invention, glass substrates with a thickness of 0.05 mm to 4 mm can be used.
[0022] Before the layer deposition takes place, the glass substrate 101 is heated to a temperature of 330°C to 400°C by means of a heating device 105. In the exemplary embodiment, the heating device 105 is designed as a radiant heater. For this purpose, for example, a radiant heater can be used which has a surface temperature of 500°C to 580°C and an emissivity greater than 0.8. Such a radiant heater is particularly suitable for heating glass substrates with a thickness of 0.05 mm to 2 mm. Alternatively, the glass substrate 101 can also be heated by means of one or more heating rollers over which the glass substrate 101 is guided.
[0023] After the glass substrate 101 has been heated, it is guided past the coating device 103. In one embodiment of the invention, a thermochromic vanadium dioxide layer with a layer thickness of 45 nm to 80 nm is deposited by means of the coating device 103. The coating device 103 comprises at least one target consisting of vanadium or vanadium oxide and at least one magnetron with which the target is sputtered. In addition to vanadium or vanadium oxide, the at least one target can also have one or more metallic doping elements with which the deposited thermochromic vanadium dioxide layer is to be doped, for example in order to set a desired transition temperature of the thermochromic vanadium dioxide layer. The doping can, for example, amount to up to two atomic percent of the target material. Alternatively, it is also possible to dope the doping element orto sputter the doping elements using a separate target next to the vanadium or vanadium oxide target. Such a deposition process is also referred to as co-sputtering. Tungsten, in particular, has achieved particular importance as a doping element for thermochromic vanadium dioxide layers. In the method according to the invention, however, in addition to tungsten, chromium, molybdenum, cerium, niobium, or magnesium can also be used as suitable doping elements. The layer deposition process in the method according to the invention is designed as a reactive process. For this purpose, the reactive gas oxygen is admitted into the working chamber through at least one inlet 106, and the amount of oxygen flowing into the working chamber is regulated by means of a valve 107.
[0024] The device 100 also comprises at least one lighting device 108, which is arranged downstream of the coating device 103 on one side of the coated glass substrate 101. The lighting device 108 emits light radiation that is detectable by the human eye. The lighting device 108 is aligned such that the emitted light radiation penetrates the coated glass substrate 101. A first sensor 109 is arranged on the other side of the glass substrate 101, with which a first actual value can be detected, which characterizes the transmission of the light radiation penetrating the coated glass substrate 101. The detected first actual value for the transmission of the light radiation is forwarded to an evaluation device (not shown in Fig. 1) and compared there with a first target value for the transmission of the light radiation, thus producing a first comparison result.Depending on the first comparison result, the flow rate of the reactive gas oxygen through inlet 106 into the working chamber is then regulated by valve 107. If the first actual value is greater than the first setpoint, the flow rate of the reactive gas oxygen flowing through inlet 106 is reduced. If, however, the first actual value is less than the first setpoint, the flow rate of the reactive gas oxygen flowing through inlet 106 is increased.
[0025] According to the invention, a second control loop is also formed for adjusting the amount of oxygen flowing into the working chamber. For this purpose, a second sensor 110 is arranged downstream of the coating device 105, viewed in the direction of movement of the glass substrate, with which a second actual value can be detected that characterizes the temperature of the coated glass substrate 101. The detected second actual value for the temperature of the coated glass substrate 101 is forwarded to the evaluation device, where it is compared with a second target value for the temperature of the coated glass substrate 101, thus producing a second comparison result. Depending on the second comparison result, the flow rate of the reactive gas oxygen through the at least one inlet 106 into the working chamber is then regulated by means of the valve 107. In the process, the flow rate of the reactive gas oxygen is increased.if the second actual value is higher than the second setpoint or the flow rate is reduced if the second actual value is lower than the second setpoint.
[0026] The second sensor 110 can be designed, for example, as a pyrometer and is preferably arranged on the uncoated side of the glass substrate 101. The second sensor should be arranged as close as possible to the coating device 103. In one embodiment, the second sensor is arranged at a distance of 0.1 m to 0.5 m from the coating device 103 but still in front of the first sensor 109.
[0027] The inventive interaction of two control loops for adjusting the flow rate of the reactive gas oxygen into the working chamber, taking into account two physical parameters that can be used to characterize the layer properties, makes it possible to deposit thermochromic vanadium dioxide layers with homogeneous layer properties even on large-area glass substrates. A rough adjustment of the oxygen gas flow rate is performed using the first control loop, incorporating the first sensor 109, and a finer adjustment of the oxygen gas flow rate is performed using the second control loop, incorporating the second sensor 110.
Claims
Patent claims 1. A method for depositing a thermochromic vanadium dioxide layer on a glass substrate (101) within a working chamber, wherein a) the glass substrate (101) is guided past a coating device (103) within the working chamber; b) oxygen is admitted into the working chamber through at least one inlet (106); c) the glass substrate (101) is heated by means of at least one heating device (105) before the layer deposition; d) a target made of vanadium or vanadium oxide is sputtered by means of at least one magnetron within the coating device (103); e) after the layer deposition, light radiation which is detectable by a human eye is emitted by means of at least one lighting device (108) arranged on one side of the glass substrate (101); a first actual value for the transmission of the light radiation is detected by means of a first sensor (109) on the other side of the glass substrate (101);within an evaluation device, the first actual value for the transmission is compared with a first target value for the transmission and, depending on the result of this first comparison, the oxygen flow through the at least one inlet (106) into the working chamber is regulated, characterized in that f) after the layer deposition, before the first sensor (109), a second actual value for the temperature of the glass substrate (101) is detected by means of a second sensor (110), compared within the evaluation device with a second target value for the temperature of the glass substrate (101), and, depending on the result of the second comparison, the oxygen flow through the at least one inlet (106) into the working chamber is regulated.; 2. Method according to claim 1, characterized in that a plate-shaped or strip-shaped substrate is used as the glass substrate (101).
3. Method according to claim 1 or 2, characterized in that a radiant heater or a heating roller over which the glass substrate (101) is guided is used as the heating device (105).
4. Method according to one of the preceding claims, characterized in that the glass substrate (101) is heated by means of the heating device (105) to a temperature in a range of 330 °C to 400 °C.
5. Method according to one of claims 1 to 4, characterized in that a target made of vanadium or vanadium oxide is used, in which the target material has a doping of a metal of up to two atomic percent.
6. Method according to one of claims 1 to 4, characterized in that a doping material is deposited by means of co-sputtering.
7. Method according to claim 5 or 6, characterized in that a material is used for the doping which comprises at least one of the elements tungsten, chromium, molybdenum, cerium, niobium or magnesium.
8. Method according to one of the preceding claims, characterized in that a pyrometer is used as the second sensor (1 10), which is arranged on the side of the glass substrate not to be coated.
9. Method according to one of the preceding claims, characterized in that the second sensor (1 10) is arranged at a distance of 0.1 m to 0.5 m after the coating device.
10. Method according to one of the preceding claims, characterized in that a glass substrate (101) with a thickness of 0.05 mm to 4 mm is used.