Volume-controlled Fabry-Perot interferometer

Abstract

The present disclosure describes a capacitively controlled Fabry-Perot interferometer including a first mirror layer having a first thin-film metal layer embedded in a first insulating layer and a second mirror layer having a second thin-film metal layer embedded in a second insulating layer. A control region in the first thin-film metal layer is at least partially aligned in an actuation direction with a control region in the second thin-film metal layer. The interferometer also includes a first control electrode and a first dielectric layer, the first dielectric layer being between the first control electrode and at least a portion of the control region of the first thin-film metal layer.

Description

[Technical Field]

[0001] The present disclosure relates to a Fabry-Perot optical filter, and in particular to a micromechanical Fabry-Perot interferometer. The present disclosure further relates to a mechanism by which the gap between a top mirror and a bottom mirror can be controlled. [Background technology]

[0002] A micromechanical Fabry-Perot interferometer typically comprises a top mirror suspended above a bottom mirror above a substrate. The two mirrors are separated from each other by a mirror gap, such that an optical tuning cavity is formed between the two mirrors. The two mirrors are at least partially transparent. Incident electromagnetic radiation can enter the tuning cavity from one side and exit the tuning cavity from the other side.

[0003] Light entering an optical cavity can undergo multiple reflections between the bottom and top mirrors before being transmitted from the cavity. Constructive interference produces a transmission peak at a wavelength corresponding to the equation 2d=nλ, where d is the mirror gap height and n is an integer. The first-order transmission peak, corresponding to n=1, is accompanied by higher-order transmission peaks from wavelengths that satisfy the equation when n is greater than 1. Order-selective filters can be implemented using Fabry-Perot filters to allow transmission only for wavelengths corresponding to one specific value of n.

[0004] Micromechanical Fabry-Perot interferometers can be configured to filter electromagnetic radiation over a wavelength range extending from visible light to infrared. The transmission wavelength can be selected by adjusting the mirror gap. Some microelectromechanical Fabry-Perot filters utilize MEMS actuators to move one mirror relative to the other, thereby adjusting the mirror gap. U.S. Patent Application Publication No. 2009153844 discloses a MEMS Fabry-Perot filter in which an electrostatic actuator is connected to one mirror. The challenge with this actuation mechanism is that the actuator consumes a lot of surface area and requires many additional processing steps. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] US Patent Application Publication No. 2009153844 Summary of the Invention

[0006] An object of the present disclosure is to provide an apparatus that overcomes the above problems.

[0007] The object of the disclosure is achieved by a configuration characterized by what is stated in the independent claims. Preferred embodiments of the disclosure are presented in the dependent claims.

[0008] This disclosure is based on the idea that the relative motion between the bottom and top mirrors is actuated by a direct electrostatic attraction between the two mirrors. The potential of at least one of the two mirrors is set via a capacitively coupled control electrode. The advantage of this configuration is that the mirror gap can be adjusted with high precision over a wide range. [Brief explanation of the drawings]

[0009] In the following, the present disclosure will be described in more detail by way of preferred embodiments with reference to the accompanying drawings.

[0010] [Figure 1a] 1 shows a volume-controlled Fabry-Perot interferometer. [Figure 1b] A ring-shaped control region in the xy plane is shown. [Figure 1c] 1 shows an equivalent circuit for the device shown in FIG. 1a. [Figure 1d] A device is shown in which one control electrode is in direct electrical contact with the thin metal layer. [Figure 2] A device is shown in which a semi-insulating layer allows charge to be transferred between the mirror layers. [Figure 3a] 1 shows a method for fabricating a volume-controlled Fabry-Perot interferometer. [Figure 3b] 1 shows a method for fabricating a volume-controlled Fabry-Perot interferometer. [Figure 3c] 1 shows a method for fabricating a volume-controlled Fabry-Perot interferometer. [Figure 3d] 1 shows a method for fabricating a volume-controlled Fabry-Perot interferometer. [Figure 3e] 1 shows a method for fabricating a volume-controlled Fabry-Perot interferometer. [Figure 3f] 1 shows a method for fabricating a volume-controlled Fabry-Perot interferometer. [Figure 3g] 1 shows a method for fabricating a volume-controlled Fabry-Perot interferometer. DETAILED DESCRIPTION OF THE INVENTION

[0011] The present disclosure describes a volumetrically controlled Fabry-Perot interferometer, which includes a first mirror layer including a first thin-film metal layer embedded in a first insulating layer, the first thin-film metal layer including a central region and a control region.

[0012] The interferometer also includes a second mirror layer including a second metal thin film layer embedded in a second insulating layer. The second metal thin film layer includes a central region and a control region. The central region of the first metal thin film layer is at least partially aligned in the actuation direction with the central region of the second metal thin film layer. The control region of the first metal thin film layer is at least partially aligned in the actuation direction with the control region of the second metal thin film layer.

[0013] The interferometer also includes a first control electrode and a first dielectric layer. The first dielectric layer is between the first control electrode and at least a portion of the control region of the first thin-film metal layer. The first dielectric layer is part of the first insulating layer in which the first thin-film metal layer is embedded. The interferometer also includes a second control electrode electrically coupled to the control region of the second thin-film metal layer.

[0014] The first mirror layer may be fixed to a substrate, and the second mirror layer may be suspended above the substrate so that the two mirror layers are substantially parallel to each other. The term "actuation direction" refers to the direction of operation of the interferometer. Electromagnetic radiation filtered by the interferometer enters and exits the interferometer in the actuation direction. The actuation direction may be, for example, substantially perpendicular to the surfaces of the first and second mirror layers and the substrate.

[0015] When the plane of the substrate is used to define a horizontal plane, the actuation direction may be referred to as the vertical direction, the first mirror layer may be referred to as the bottom mirror, and the second mirror layer may be referred to as the top mirror. However, the terms "top / bottom" or "up / down" as used in this disclosure refer only to how the device is oriented when fabricated. Because the device can be oriented in any direction when in use, the "actuation direction" is not necessarily vertical when the device is in use.

[0016] FIG. 1a shows a capacitively controlled Fabry-Perot interferometer having a first mirror layer 11. The first mirror layer includes a first thin-film metal layer 111 embedded in a first insulating layer 112. Correspondingly, the second mirror layer 12 includes a second thin-film metal layer 121 embedded in a second insulating layer 122. In this case, the second mirror layer 12 rests on a substrate 18, while the first mirror layer 11 is suspended above the substrate by two spacers 141 and 142, thereby forming a tuning cavity 17 between the first and second mirror layers. The substrate 18 may be, for example, a fused silica substrate or a sapphire substrate, or any other suitable substrate sufficiently transparent to the radiation the interferometer is designed to pass.

[0017] The substrate defines an xy plane, indicated by the x-axis in Figure 1a. The actuation direction is indicated here by the z-axis, and the height of the cavity 17 in the actuation direction is the mirror gap 171. The mirror gap is adjustable by an actuation force that moves the first mirror layer 11 relative to the second mirror layer 12, as described below.

[0018] The spacers 141 and 142 can be made from an oxide layer, such as a layer of tetraethyl orthosilicate (TEOS), deposited at a relatively low temperature. Alternatively, they can be made from a polymer layer. The thickness of this oxide or polymer layer typically determines (or may be equal to) the initial height of the mirror gap 171 before an actuation force is applied. The thickness of the layer forming the spacers 141 and 142 can be, for example, in the range of 200 nm to 4 μm. The optimal thickness depends, among other things, on the desired passband wavelength of the interferometer.

[0019] The first and second metal thin film layers 111 and 121 are electrically conductive and function as reflectors in each mirror layer. The layers 111 and 121 may be made of, for example, silver, gold, platinum, or titanium. The thickness of the first and second metal thin film layers 111 and 121 may be in the range of 30 nm to 50 nm, or in the range of 15 nm to 60 nm.

[0020] The insulating layers 112 and 122 with the embedded metal thin film must have a sufficiently high tensile stress to flexibly accommodate the bending experienced by the first mirror layer 11 when an actuation force narrows the mirror gap by bringing the first mirror layer 11 closer to the second mirror layer 12. The insulating layers 112 and 122 may be, for example, Al2O3 layers, and their thickness may be, for example, in the range of 5 to 100 nm.

[0021] Dotted lines 191-196 divide the device into five regions along the x-axis. Both the first and second mirror layers 11 and 12 have central regions at regions 191-192. The first mirror layer 11 has a first control region at regions 192-196 and a second control region at regions 191-193. The second mirror layer 12 has a first control region at regions 195-191 and a second control region at regions 192-194. The first and second metal thin film layers have central regions and control regions corresponding to the central regions and control regions of the first and second mirror layers, respectively.

[0022] The first and second metal thin-film layers 111 and 121 may extend as continuous layers from 193 to 196 and 195 to 194, respectively. However, it is typically more beneficial to separate the central regions of the metal thin-film layers from their control regions. In other words, the first and second metal thin-film layers 111 and 121 may be discontinuous. The central portions of these layers within regions 191-192 may be electrically floating, while the control portions within control regions 193-191 and 192-194 may be set to specific potentials via capacitively or ohmically coupled control electrodes in capacitive or direct electrical contact with the control regions.

[0023] The first and second control regions of the first mirror layer 11 shown in Figure 1a may be part of a continuous first ring-shaped control region. The first and second control regions of the second mirror layer 12 may correspondingly be part of a continuous second ring-shaped control region. The second ring-shaped control region may be aligned with the first ring-shaped control region in the actuation direction.

[0024] FIG. 1b shows a ring-shaped control region in the xy plane. The first and second ring-shaped control regions overlap within this control region. This control region may have a donut shape. The cross section shown in FIG. 1a is taken along line AA in FIG. 1b. This control region geometry keeps the central region of the first mirror layer 11 parallel to the central region of the second mirror layer 12 when the first mirror is actuated in the actuation direction. Other control region geometries are possible.

[0025] The central region of the first mirror layer 11 may be larger than the central region of the second mirror layer 12, or vice versa. The first and second ring-shaped control regions of the two mirror layers also have different sizes. Nevertheless, the central region of the first mirror layer 11 must be at least partially aligned with the central region of the second mirror layer 12 in the actuation direction, so that they overlap in the xy plane. The overlapping area forms the optically active region of the interferometer. The control region of the first mirror layer is also at least partially aligned with the control region of the second mirror layer in the actuation direction, so that they overlap in the xy plane. This overlapping area can have, for example, the donut shape described above, or any other suitable shape.

[0026] The overlapping region of the control regions forms the actuation region. In this region, a potential difference between the control regions of the metal thin film layers 111 and 121 generates an electrostatic attraction between the mirror layers 11 and 12. The first and second metal thin film layers may be made of, for example, silver, which has good electrical conductivity and typically also good reflectivity in the wavelength region of most interest. Any of the other materials described below may also be used for the first and second metal thin film layers.

[0027] In the device shown, where the first mirror layer 11 is suspended over a substrate and the second mirror layer is fixed to the substrate 18, this attractive force pulls the first mirror layer 11 towards the substrate 18. This narrows the mirror gap 171 and changes the wavelength of radiation that can pass through the interferometer. Because the magnitude of the potential difference determines the magnitude of the electrostatic attractive force, the first mirror layer 11 can be moved up or down by changing the potential difference.

[0028] In a different device (not shown) in which both mirror layers are suspended to allow movement in the actuation direction, the mirror gap 171 can be narrowed / widened by the relative movement of the two mirror layers towards / away from each other, respectively.

[0029] The interferometer includes a first control electrode 131 separated from a control region of the first metal thin film layer 111 by a first dielectric layer. This forms a first control capacitance between the first control electrode 131 and the first metal thin film layer 111. In the device shown in FIG. 1a, the first insulating layer 112 forms the first dielectric layer in the capacitor. In other words, the first control electrode 131 is disposed above the first insulating layer 112 in the portion of the control region bounded by 194 and 196. In other words, the first dielectric layer is formed by the first insulating layer 112 with the first metal thin film layer embedded in it. If the first dielectric layer includes multiple sublayers deposited on top of each other, the first dielectric layer may be formed by one of these sublayers. The first dielectric layer still forms part of the first insulating layer.

[0030] If a first dielectric layer having a different thickness is preferred, an additional dielectric layer (not shown) can be added in regions 194-196 before first control electrode 131 is deposited. This additional dielectric layer can be disposed above first insulating layer 112 in FIG. 1a or directly above thin-film metal layer 111 if the first insulating layer does not extend into regions 194-196. Other variations are possible. First control electrode 131 can, for example, be deposited on substrate 18 in regions 194-196, and then the control electrode can be separated from the first thin-film metal layer by both the first dielectric layer and spacers 142.

[0031] In other words, a control capacitor is formed in the region where each control electrode and the corresponding metal thin film layer overlap. The dielectric of each control capacitor is formed by at least a first insulating layer surrounding the metal thin film layer, and may additionally include other laminated dielectric layers such as a spacer and a second insulating layer.

[0032] The interferometer also includes a second control electrode 132 electrically coupled to the control region of the second mirror layer 12. This electrical coupling can be capacitive or Ohm's law. Figure 1a shows an interferometer in which the second control electrode 132 is capacitively coupled. The interferometer includes a second dielectric layer between the second control electrode and at least a portion of the control region of the second metal thin-film layer, such that the second control electrode is capacitively coupled to the control region of the second metal thin-film layer. The second dielectric layer is part of the second insulating layer 122 in which the second metal thin-film layer is embedded. The options discussed above for the first dielectric layer also apply to the second dielectric layer. This forms a second control capacitance between the second control electrode 132 and the second thin-film layer 121. The first and second control electrodes 131 and 132 can be, for example, layers of aluminum.

[0033] In FIG. 1a, spacer 141 is above the second dielectric layer in a portion of the control region of the second mirror layer delimited by lines 195 and 193. Here, insulating layers 112 and 122 are also between second control electrode 132 and second thin-film metal layer 121. Thus, both first and second control electrodes 131 and 132 are above first insulating layer 112 in FIG. 1a. Between second control electrode 132 and second thin-film metal layer 121 are all first and second insulating layers, as well as spacer 141. In other words, in FIG. 1a, first mirror layer 11 forms the top mirror, and second mirror layer 12 forms the bottom mirror, and first and second control electrodes 131 and 132 are above first mirror layer 11.

[0034] Alternatively, the spacer 141 and some or all of the first insulating layer 112 can be removed in the portion of the control region bounded by the lines 195-193 so that the second control electrode 132 can be positioned closer to the second metal thin film layer 121. In either case, the second control electrode 132 is still separated from the second metal thin film layer 121 by a dielectric layer that is at least part of the second insulating layer 122 in which the second metal thin film layer 121 is embedded. The optimal thicknesses of both the first and second dielectric layers depend on the desired capacitances of the first and second control capacitors. These desired capacitances do not necessarily have to be equal.

[0035] Figure 1c shows an equivalent circuit for the device shown in Figure 1a. The circuit includes a main control capacitor C formed between the control regions of the first and second mirror layers in regions 193-191 and 192-194 and all of the overlap regions shown in Figure 1b. Control First and second control capacitors C coupled in series with s1 and C s2 This allows the two fixed capacitors C connected in series with the main control capacitor. s1 and C s2An AC voltage can be coupled between the first metal thin film layer 111 and the second metal thin film layer 121 via the first and second control capacitors. Typical capacitances of the first and second control capacitors are in the pF range.

[0036] In the arrangement shown in Figure 1a, C s1 is typically C s2 Much larger than C s2 is C Control Substantially equal to or less than C s2 If is sufficiently small, this fixed capacitor limits the strength of the electric field generated between the control regions of the two thin metal layers (i.e., limits the electric field acting on the main control capacitor). As the mirror gap narrows, the strength of the electric field does not increase dramatically in proportion to the inverse of the mirror gap. Instead, the fixed capacitor facilitates a higher level of increase, which allows the mirror gap to be narrowed very narrowly, by as much as two-thirds from its rest position, without the risk of snapping the two mirrors together.

[0037] If the material in the second dielectric layer 141 is, for example, silicon dioxide with a relative dielectric constant of 3.8, and the overlap area shown in FIG. 1b is 3.8 times the surface area of ​​the second control capacitor in the region between 195 and 193, a theoretical tuning range of 66% of the mirror gap from the rest position can be achieved, and the wavelength passing through the interferometer can be tuned in the range of 300 nm to 3000 nm by constructive interference.

[0038] Figure 1d shows an alternative device in which the second control electrode is in direct electrical contact with the second metal layer within the control region of the second metal layer, resulting in the second control electrode being ohmically coupled to the control region of the second mirror layer. In this case, the other control electrode is capacitively coupled to form a series capacitance, which allows for optimal control characteristics of the Fabry-Perot device.

[0039] All reference numerals in Figure 1d refer to the same device components as in Figure 1a, and the same materials listed above can be used for each component. The only difference is that the second control electrode 132 in Figure 1d is located directly above the second metal thin-film layer 121 in the control region of the second mirror layer between 195 and 193. This arrangement can, in some cases, simplify the required drive electronics. In Figure 1d, the first mirror layer 11 forms the top mirror, the second mirror layer 12 forms the bottom mirror, the first control electrode 131 is above the first mirror layer 11, and the second control electrode 132 is in an opening that extends down to the second metal thin-film layer 121.

[0040] The capacitive actuation control described above can result in the accumulation of static charge on the metal thin film layer during use. This can create a DC voltage between the first and second metal thin film layers, potentially disrupting operation of the device. To avoid problems caused by static charge, an additional semi-insulating layer can be in contact with the metal thin film layer. The first metal thin film layer can be in direct electrical contact with the second metal thin film layer through one or more semi-insulating layers at one or more short circuit points.

[0041] The frequency of the AC actuation voltage applied to the control electrodes is typically very high so that the presence of the semi-insulating layer does not affect the actuation force, but a DC voltage is avoided if electrostatic charge can be discharged through the semi-insulating layer and / or equalized between the first and second mirror layers.

[0042] The first mirror layer may include a first semi-insulating layer embedded within the first insulating layer in direct electrical contact with the first thin-film metal layer. The second mirror layer may include a second semi-insulating layer embedded within the second insulating layer in direct electrical contact with the second thin-film metal layer. The first semi-insulating layer may be in direct electrical contact with the second semi-insulating layer at one or more short points.

[0043] The first and second semi-insulating layers may, for example, be thin, at least partially transparent semiconductor oxide layers, such as titanium dioxide or indium tin oxide. Figure 2 shows an interferometer in which reference numerals 211-212, 221-222, 231-232 and 241-242 correspond to reference numerals 111-112, 121-122, 131-132 and 141-142 in Figure 1a, respectively.

[0044] 2 also includes a first semi-insulating layer 251 covering the first thin-film metal layer 211 in both its central and control regions. Correspondingly, a second semi-insulating layer 252 covers the second thin-film metal layer 221 in both its central and control regions.

[0045] The first and second semi-insulating layers 251 and 252 also extend outside the control region to shorting points 261 and 262 where they are in electrical contact with each other. In this case, each shorting point includes a conductive via extending through the corresponding spacer 241 / 242, although the shorting points may alternatively include only points where the layers 251 and 252 are in direct contact with each other. The conductivity of the first and second semi-insulating layers 251 and 252 is sufficient to prevent the generation of DC fields caused by static charges across the optical cavity.

[0046] Alternatively, the semi-insulating layers 251 and 252 extending across the optically active region may be omitted, and the shorting point may instead include a via made from semi-insulating material. The formation of a DC electric field between the first and second thin-film metal layers 211 and 221 is then prevented by charge equalization occurring across these semi-insulating vias.

[0047] The semi-insulating layer may also be placed in contact with the thin metal film layers of the device shown in FIG. 1d, and they may be shorted in the manner described above. Alternatively or complementary to any of the above-described embodiments, it is possible to prevent the formation of a DC electric field between the first and second thin metal film layers by depositing a layer of semi-insulating material on the top, bottom, and sidewalls of the tuning cavity formed between the first and second mirror layers. The layer of semi-insulating material then covers the top, bottom, and sidewalls of the tuning cavity, forming a Faraday cage within the tuning cavity in which no DC fields are present. Another alternative or complement to any of the above-described embodiments is that a layer of semi-insulating material can be deposited on top of the entire device of FIG. 1a, FIG. 1d, or FIG. 2. The layer of semi-insulating material then overlies both the control electrode and the first mirror layer 11.

[0048] This disclosure also describes a method for fabricating a capacitively controlled Fabry-Perot interferometer on a substrate, as shown in Figures 3a-3g. Substrate 38 includes a first capacitor region 391, a second capacitor region 395, a central region 393 between first capacitor region 391 and second capacitor region 395, a first control region 392 between first capacitor region 391 and central region 393, and a second control region 394 between central region 393 and second capacitor region 395. This is shown in Figure 3a.

[0049] The method includes depositing a first lower layer 3221 of insulating material over a substrate 38, and then depositing a lower metal thin film layer 3211 over the first lower layer 3221 of insulating material. This is shown in FIG. 3a. The method also includes patterning the lower metal thin film layer 3211 to extend to a first capacitor region 391, a first control region 392, a central region 393, and a second control region 394, as shown in FIG. 3b, and then depositing a second lower layer 3222 of insulating material over the lower metal thin film layer 3211. The second lower layer 3222 of insulating material may comprise the same insulating material as the first lower layer 3211 of insulating material. Alternatively, the second lower layer 3222 may comprise a different insulating material, such that the corresponding insulating layer in which the metal thin film layer is embedded is made of two sublayers of different materials.

[0050] The method then includes depositing a layer of spacer material 34 over the second lower layer of insulating material 3222, depositing a first upper layer of insulating material 3121 over the layer of spacer material 34, and depositing an upper thin-film metal layer 3111 over the first upper layer of insulating material 3121. The method then includes patterning the upper thin-film metal layer 3111 to extend to the first control region 392, the central region 393, the second control region 394, and the second capacitor region 395. These steps are shown in Figures 3c and 3d.

[0051] The method also includes depositing a second, upper layer 3122 of insulating material above the upper metal thin film layer 3111, as shown in Figure 3d. The second, upper layer 3122 of insulating material may comprise the same insulating material as the first, upper layer 3121 of insulating material, or may comprise a different insulating material, such that the insulating layer in which the metal thin film layer is embedded consists of two sub-layers of different materials.

[0052] The method also includes depositing a layer 33 of conductive material above the second upper layer 3122 of insulating material, and patterning the layer 33 of conductive material to form a first control electrode 331 in the first capacitor region and a second control electrode 332 in the second capacitor region, where the first control electrode 331 is electrically isolated from the second control electrode 332. These steps are shown in Figures 3e and 3f.

[0053] Finally, the method also includes forming inlet holes 35 in the first and second upper layers 3121-3122 of insulating material and the upper metal thin film layer 3111 in at least the central region 393, and etching away the spacer material 34 down to the second lower layer 3222 of insulating material with an etchant that reaches the spacer material 34 through the inlet holes 35, thereby forming a tuning cavity 37 below the first upper layer of insulating material 3121 in the central region 393 and the first and second control regions 392, 394. These steps are shown in FIG. 3g. This forms the tuning cavity 37 between the second lower layer 3222 of insulating material and the first upper layer 3121 of insulating material.

[0054] This method minimizes the masking and etching steps required for the fabrication of a capacitively controlled Fabry-Perot interferometer. The method shown in Figures 3a-3g allows both control electrodes 331 and 332, connected to external circuitry, to be easily and reliably formed on the top surface of the device. This advantage can also be achieved in the device shown in Figure 1d if electrode 131 is placed in direct contact with metal thin-film layer 111 (instead of contacting 132 with 121, as shown).

[0055] Reference numerals 31, 311-312, 32, 321-322, 331-332, 341-342 and 37 in Figures 3f and 3g correspond to reference numerals 11, 111-112, 12, 121-122, 131-132, 141-142 and 17 in Figure 1a, respectively.

[0056] The layer of insulating material 3221 may be deposited, for example, by atomic layer deposition (ALD), and the layer of metal thin film material may be deposited by sputtering or any other suitable method. The spacer material may be deposited by a PECVD process. The materials and thicknesses of these layers may be any of the alternatives previously described in this disclosure.

[0057] In the manufacturing process described above, a thin metal layer is embedded in an insulator to form the first and second mirror layers 31 and 32. Patterning of the thin metal layer is optional, as described above, and this layer may alternatively be a continuous layer. If the material used for the thin metal layer is sensitive to the patterning process, an additional protective layer may be applied over these layers before they are patterned. This option is not shown.

[0058] The etchant used to form the tuning cavity 37 may be, for example, hydrogen fluoride. The sizes of the entrance holes 35 are exaggerated for clarity, and their size in the xy plane may actually be smaller relative to the dimensions of the mirror.

[0059] The semi-insulating layer shown in FIG. 2 may optionally be included in the manufacturing process, for example by ALD deposition, at an appropriate stage in the process.

Claims

1. 1. A volume-controlled Fabry-Perot interferometer, comprising: a first mirror layer comprising a first thin-film metal layer embedded in a first insulating layer, said first thin-film metal layer acting as a reflector in said first mirror layer and said first thin-film metal layer comprising a central region and a control region; a second mirror layer comprising a second metal thin film layer embedded in a second insulating layer, said second metal thin film layer acting as a reflector in said second mirror layer and comprising a central region and a control region, said central region of said first metal thin film layer being at least partially aligned in an actuation direction with said central region of said second metal thin film layer, and said control region of said first metal thin film layer being at least partially aligned in an actuation direction with said control region of said second metal thin film layer; a first control electrode and a first dielectric layer, the first dielectric layer being between the first control electrode and at least a part of the control area of ​​the first metal thin film layer so that a first control capacitance is formed between the first control electrode and the first metal thin film layer, the first dielectric layer being part of the first insulating layer in which the first metal thin film layer is embedded, and the first control electrode being arranged above the first mirror layer; a second control electrode electrically connected to the control region of the second metal thin film layer, the second mirror layer is on a substrate, and the first mirror layer is suspended above the substrate by two spacers, thereby forming a tuning cavity between the first mirror layer and the second mirror layer; a second dielectric layer between the second control electrode and at least a portion of the control region of the second metal thin film layer, such that a second limiting capacitance is formed between the second control electrode and the second metal thin film layer; one of the spacers is between the second control electrode and the second metal thin film layer; and the second control electrode is above the first mirror layer.

2. 2. A capacitively controlled Fabry-Perot interferometer as defined in claim 1, wherein said second control electrode is in direct electrical contact with said second thin-film metal layer in a control region of said second thin-film metal layer.

3. 3. A capacitively controlled Fabry-Perot interferometer according to claim 1, wherein the first metal thin film layer is in direct electrical contact with the second metal thin film layer at one or more short-circuit points via one or more semi-insulating layers.

4. 4. The capacitively controlled Fabry-Perot interferometer of claim 3, wherein the first mirror layer comprises a first semi-insulating layer in direct electrical contact with the first thin-film metal layer and embedded within the first insulating layer, the second mirror layer comprises a second semi-insulating layer in direct electrical contact with the second thin-film metal layer and embedded within the second insulating layer, and the first semi-insulating layer is in direct electrical contact with the second semi-insulating layer at the one or more short points.

5. 5. A capacitively controlled Fabry-Perot interferometer according to claim 1, wherein a layer of semi-insulating material covers the top, bottom and sidewalls of a tuning cavity formed between the first and second mirror layers.

6. 6. A volume-controlled Fabry-Perot interferometer according to claim 1, wherein the first and second thin metal layers are made of silver.

7. 1. A method for fabricating a capacitively controlled Fabry-Perot interferometer on a substrate including a first capacitor region, a second capacitor region, a central region between the first capacitor region and the second capacitor region, a first control region between the first capacitor region and the central region, and a second control region between the central region and the second capacitor region, comprising: - depositing a first lower layer of insulating material on said substrate; - depositing a lower metal thin film layer above said first lower layer of insulating material; - patterning the lower metal thin film layer to extend over the first capacitor region, the first control region, the central region, and the second control region; - depositing a second lower layer of insulating material above said lower metal thin film layer, said second lower layer of insulating material comprising the same insulating material as said first lower layer of insulating material; - depositing a layer of spacer material above said second lower layer of insulating material; - depositing a first upper layer of insulating material above said layer of spacer material; - depositing an upper metal thin film layer above said first upper layer of insulating material; - patterning the upper metal thin film layer to extend over the first control region, the central region, the second control region, and the second capacitor region; - depositing a second upper layer of insulating material above the upper metal thin film layer, the second upper layer of insulating material comprising the same insulating material as the first upper layer of insulating material; - depositing a layer of conductive material above said second upper layer of insulating material; - patterning the layer of conductive material to form a first control electrode in the first capacitor area and a second control electrode in the second capacitor area, the first control electrode being electrically isolated from the second control electrode; - forming inlet holes in the first and second upper layers of insulating material and in the upper metal thin film layer, at least in the central region; forming tuning cavities below the first upper layer of insulating material in the central region and the first and second control regions by etching away the spacer material down to the second lower layer of insulating material using an etchant that reaches the spacer material through the inlet holes.

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