Timepiece component colored by interference effect

Abstract

The invention relates to a timepiece component comprising a base plate (2), a first interference layer (4) in direct or indirect contact with the base plate (2), and a second interference layer (3) covering the first interference layer (4), the first interference layer (4) being characterized in that it has a thickness of between 3 nm and 250 nm and is made of a first material that is optically transparent in the visible range of 380 nm to 780 nm, the refractive index n of the first material being less than or equal to 2 throughout said visible range, the second interference layer (3) being characterized in that it has a thickness of between 3 nm and 80 nm and is made of a second material whose refractive index n and absorption coefficient k reach values greater than or equal to 3 and greater than or equal to 0.5, respectively, in at least part of said visible range.

Description

Technical Field

[0001] This invention relates to watch components colored by interference effects, and more particularly to balance wheels and hairsprings colored by interference effects. Background Technology

[0002] Typically, certain metal alloy balance springs used in watches are blued to enhance their appearance and corrosion resistance. With the advent of silicon balance springs, which include a silicon oxide outer layer (which provides the silicon balance spring with suitable mechanical properties to compensate for the watch's operating temperature), the use of blue balance springs has decreased. In fact, the functionality of balance spring assemblies has surpassed their aesthetics. When initially developed, these balance springs comprised a single layer of silicon oxide more than one micrometer thick, known as a temperature compensation layer, giving the balance spring a light gray hue. Later, to counteract electrostatic effects and humidity, the balance spring was plated with a metallic layer, giving it a metallic appearance.

[0003] US Patent 2022 / 0004149 discloses a black photovoltaic device. Conventional thin-film amorphous silicon solar cells have an eggplant-like red color because they reflect light with wavelengths greater than approximately 650 nm. This color is generally considered unattractive and therefore undesirable in the watchmaking industry, particularly for watch dials. To address this issue, the patent provides a photovoltaic device comprising: a conductive front contact layer; a conductive back contact layer located further away from the incident light source than the front contact layer; and a semiconductor-based PIN junction comprising a fundamentally amorphous intrinsic silicon layer sandwiched between a p-type doped semiconductor layer and an n-type doped semiconductor layer. According to the invention, the layer closest to the back contact layer in the PIN junction is a silicon-germanium alloy layer containing at least 2 mol% germanium. This silicon-germanium alloy is capable of absorbing visible light in the red wavelength range (which is the wavelength range typically transmitted by amorphous silicon-based devices). This results in a deep black photovoltaic device, overcoming the red, eggplant-purple, or purple hues commonly found in amorphous silicon photovoltaic devices.

[0004] To color the visible surfaces of the balance wheel and hairspring, EP 3608728 proposes an interference coloring method. This method involves adjusting the thickness of the silicon oxide layer on the visible surface to be less than 1 µm, thereby obtaining different colors depending on the layer thickness. To ensure the required thermal compensation when the SiO2 layer thickness is greater than 1 µm, only the visible surfaces are colored. This method is relatively complex to operate, requiring adjustments to the SiO2 layer thickness based on the surface, and has the drawback that not all surfaces can be colored. Another disadvantage is that the observed color varies with the viewing angle. Summary of the Invention

[0005] The present invention aims to provide an alternative coloring method that is easy to use and capable of coloring all surfaces of the balance wheel and hairspring without being significantly affected by the viewing angle.

[0006] Therefore, it is recommended to deposit two interference layers with different optical properties on all or at least the required surfaces of the balance spring and other typical watch components.

[0007] More specifically, the present invention relates to a watch assembly comprising a substrate, a first interference layer in direct or indirect contact with the substrate, and a second interference layer covering the first interference layer, the second interference layer being oriented toward an incident light source. The first interference layer is characterized in that its thickness is 3 nm to 250 nm and is made of a first material that is spectrally transparent in the visible light range of 380 nm to 780 nm, the refractive index n of the first material being less than or equal to 2 throughout the entire visible light range. The second interference layer is characterized in that its thickness is 3 nm to 80 nm and is made of a second material whose refractive index n and absorption coefficient k are respectively greater than or equal to 3 and greater than or equal to 0.5 in at least a portion of the visible light range.

[0008] Adding a second, high-refractive-index absorbing interferometer layer to a first, low-refractive-index interferometer layer allows for the acquisition of vibrant colors while maintaining a relatively simple optical system. Furthermore, the second absorbing layer remains an interferometer layer and provides useful properties, particularly a reflection spectrum that varies minimally with the viewing angle. Therefore, a wide variety of colors can be obtained depending on the thickness of each interferometer layer.

[0009] Typically, the first interference layer of a balance wheel hairspring is a SiO2 layer, and the second interference layer is an amorphous Si layer. Another advantage of the second amorphous Si layer is that it does not absorb water, thus it can act as a moisture barrier.

[0010] The second layer can also be doped with, for example, boron or phosphorus, to form p-type or n-type micro-conductive layers, respectively. This property can be used to prevent surface charging. Attached Figure Description

[0011] Figure 1 This is a perspective view of the balance wheel and hairspring according to the present invention.

[0012] Figure 2 yes Figure 1 The cross-section of the coil on the balance wheel's hairspring is shown.

[0013] Figure 3 The schematic diagram illustrates the optical path of incident light passing through the interference layer.

[0014] Figure 4 The changes in the refractive index n and absorption coefficient k of amorphous silicon with wavelength are shown. Detailed Implementation

[0015] This invention relates to watch components that utilize interference effects for coloring. The watch component can be an external part of the watch, such as a dial, or a movement component. For example, the movement component can be a balance wheel and hairspring, an escapement wheel, or an escapement fork. The following refers to... Figure 1 The balance wheel and hairspring 1 shown herein will be described in more detail.

[0016] The watch assembly includes a substrate 2, which is wholly or partially covered by two interference layers 4 and 3. The first interference layer 4 is in direct or indirect contact with the substrate 2. The second interference layer 3 covers the first layer 4 and is used to receive incident light. The second layer 3 is made of a material with a high refractive index n and a high absorption coefficient k in the visible light range of 380 nm to 780 nm. The thickness of this layer 3 is 3 nm to 80 nm, depending on the desired interference color. The material used for this layer typically has a refractive index n and absorption coefficient k that vary with wavelength in the visible light range. For example, Figure 4 The diagram shows the variation of the refractive index *n* and absorption coefficient *k* of amorphous silicon with wavelength. According to the invention, the criteria for high refractive index *n* and high absorption coefficient *k* must be met at least in a portion of the visible light range of 380 nm to 780 nm, but not necessarily across the entire range. "High refractive index *n*" refers to a refractive index *n* value greater than or equal to 3, or even greater than or equal to 4, in at least a portion of the 380 nm to 780 nm range. Figure 4 In the example shown, it can be seen that the refractive index n is greater than 4 in the range of 380 nm to 720 nm, and greater than 3 across the entire range of 380 nm to 780 nm. "High absorption coefficient k" refers to an absorption coefficient k value greater than or equal to 0.5, or even greater than or equal to 1, in at least a portion of the 380 nm to 780 nm range. Figure 4 In the example shown, it can be seen that the absorption coefficient k is greater than 0.5 at wavelengths below 500 nm, while it is greater than 1 at wavelengths below 440 nm.

[0017] The second interference layer 3 can be, for example, a layer of amorphous silicon or amorphous germanium or alloys thereof, wherein the silicon or germanium can be alloyed, for example, with carbon or hydrogen. According to the invention, the second interference layer can be doped with boron or phosphorus to form p-type or n-type microconductive layers, respectively. Preferably, the concentration of the p-type or n-type dopant is greater than or equal to 10. 17 Atoms / cm³. Advantageously, the doped layer is deposited using plasma-enhanced chemical vapor deposition (PECVD).

[0018] A material with a high refractive index *n* and a high absorption coefficient *k* is deposited to directly contact another material with a lower refractive index *n*, thereby promoting reflection at the interface between the two materials. This is the first interference layer 4, whose thickness is typically 3 nm to 250 nm, depending on the desired color when combined with the second layer. The refractive index *n* of the material in the first layer 4 has a maximum value of 2, or even 1.5, in the range of 380 nm to 780 nm. Similarly, the refractive index *n* can vary within this range. "A maximum value of 2, or even 1.5" means that the refractive index does not exceed this value throughout the entire range of 380 nm to 780 nm. The first layer 4 also has the property of being transparent in the visible light range of 380 nm to 780 nm. For example, the first interference layer 4 can be an oxide layer, such as a silicon oxide layer, zinc oxide layer, tin oxide layer, or titanium oxide layer, or it can be a nitride layer, such as a silicon nitride layer.

[0019] The first and second layers can be deposited using methods such as plasma-enhanced chemical vapor deposition (PECVD), atomic layer deposition (ALD), and physical vapor deposition (PVD).

[0020] The first layer 4 is in direct or indirect contact with the substrate 2, which can be made of any type of material: metal, ceramic (carbide, nitride, oxide), etc. If the contact is indirect, one or more intermediate layers 5, 6 are deposited between the substrate 2 and the first layer 4. Figure 2 and Figure 3 Preferably, the refractive index of the substrate or the intermediate layer in direct contact with the first layer is different from that of the first layer. Therefore, the refractive index of the substrate or the intermediate layer in direct contact with the first layer is preferably greater than 2. More preferably, it is greater than or equal to 2.5.

[0021] for Figures 1 to 3 The balance spring 1 shown has a substrate 2 made of crystalline silicon. It is covered with a first intermediate layer 6 made of thermally compensated SiO2 with a thickness greater than 1 micrometer, followed by a metal layer 5, for example made of chromium, titanium, tantalum, or alloys thereof, with a thickness of 5 to 50 nm, for dissipating charge and preventing water absorption. This metal layer 5 is then covered with two interference layers 4 and 3, wherein the first layer 4 is made of SiO2 and the second layer 3 is made of amorphous Si.

[0022] For external components, such as a watch dial, the dial includes a crystalline silicon substrate having a first SiO2 interference layer and a second amorphous Si interference layer sequentially deposited thereon. According to one variation, the watch dial includes a solar cell having a substrate made of crystalline Si, the substrate having a first interference layer made of silicon oxide or silicon nitride (SiO2 or Si3N4) and a second interference layer made of amorphous Si sequentially deposited thereon.

[0023] Figure 3The reflected light paths at the interfaces of the first interference layer 4 and the second interference layer 3, and at the interface of the second intermediate layer 5 and the first interference layer 4, are shown. The transmission effect within the two interference layers 3 and 4 allows the interference color to vary depending on their thickness. For example, a bright blue color is obtained when the first layer is 60 nm thick and the second layer is 5 nm thick. Reducing the thickness of the first layer 4 to 30-50 nm yields a purplish color. Increasing the thickness of both layers produces a softer color.

Claims

1. A watch assembly comprising a substrate (2), a first interference layer (4) in direct or indirect contact with the substrate (2), and a second interference layer (3) covering the first interference layer (4), the second interference layer (3) facing an incident light source, the first interference layer (4) being characterized in that its thickness is 3 nm to 250 nm and is made of a first material that is spectrally transparent in the visible light range of 380 nm to 780 nm, the first material having a refractive index n less than or equal to 2 throughout the entire visible light range, the second interference layer (3) being characterized in that its thickness is 3 nm to 80 nm and is made of a second material having a refractive index n greater than or equal to 3 and an absorption coefficient k greater than or equal to 0.5, respectively, in at least a portion of the visible light range.

2. The watch assembly according to claim 1, characterized in that, Within at least a portion of the visible light range, the refractive index n and absorption coefficient k of the second interference layer (3) reach values ​​greater than or equal to 4 and greater than or equal to 1, respectively.

3. The watch assembly according to claim 1 or 2, characterized in that, The first interference layer (4) has a refractive index n of less than or equal to 1.5 throughout the visible light range.

4. The watch assembly according to claim 1 or 2, characterized in that, The first interference layer (4) is an oxide layer or a nitride layer.

5. The watch assembly according to claim 4, characterized in that, The first interference layer (4) is a SiO2 or Si3N4 layer.

6. The watch assembly according to claim 1 or 2, characterized in that, The second interference layer (3) is an amorphous Si layer, an amorphous Ge layer, or an alloy layer thereof.

7. The watch assembly according to claim 1 or 2, characterized in that, One or more intermediate layers are deposited between the substrate (2) and the first interference layer (4).

8. The watch assembly according to claim 7, characterized in that, The substrate (2) in direct contact with the first interference layer (4) or the intermediate layer in direct contact with the first interference layer (4) is made of a third material with a refractive index n greater than 2, preferably greater than or equal to 2.5, throughout the visible light range.

9. The watch assembly according to claim 1 or 2, characterized in that, The second interference layer (3) has a concentration of P-type or N-type dopants.

10. The watch assembly according to claim 9, characterized in that... The concentration of P-type or N-type dopants is greater than or equal to 10. 17 atoms / cm 3 .

11. The watch assembly according to claim 7, characterized in that, The clock assembly is a balance wheel and hairspring (1), and its crystal Si substrate (2) is sequentially plated with a first SiO2 intermediate layer (6), a second metal intermediate layer (5), a first SiO2 interference layer (4), and a second amorphous Si interference layer (3).

12. The watch assembly according to claim 1 or 2, characterized in that, The watch assembly is a dial with a crystalline Si substrate (2), which is sequentially coated with a first SiO2 interference layer (4) and a second amorphous Si interference layer (3).

13. The watch assembly according to claim 1 or 2, characterized in that, The watch assembly is a dial including a solar cell, the solar cell including a crystalline Si substrate (2), the crystalline Si substrate (2) being sequentially coated with a first SiO2 or Si3N4 interference layer (4) and a second amorphous Si interference layer (3).

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