Filter and sensor system

Abstract

The present application provides a filter having a passband partially overlapping at least a wavelength range of 800 nm to 1100 nm. The filter includes a filter stack alternately stacked by a hydrogenated silicon layer and a low refractive index layer. Each hydrogenated silicon layer has a refractive index greater than 3 in the wavelength range of 800 nm to 1100 nm and an extinction coefficient less than 0.0005 in the wavelength range of 800 nm to 1100 nm.

Description

[0001] This application is a divisional application of the divisional application 201810358341.4 with the filing date of July 16, 2013, the title of "Optical filter and sensor system"; the divisional application 201810358341.4 is a divisional application of the Chinese patent application with the filing date of July 16, 2013, the title of "Optical filter and sensor system", the application number of 201380036656.2. TECHNICAL FIELD

[0002] The present invention relates to an optical filter and a sensor system comprising the optical filter. More specifically, the present invention relates to an optical filter comprising a hydrogenated silicon layer and a sensor system comprising the optical filter. BACKGROUND

[0003] In a typical gesture recognition system, a light source emits near-infrared light to a user. A three-dimensional (3D) image sensor detects the emitted light that is reflected by the user to provide a three-dimensional image of the user. A processing system then analyzes the three-dimensional image to recognize a gesture made by the user.

[0004] With an optical filter, more specifically a bandpass filter, the emitted light is transmitted to the three-dimensional image sensor while ambient light is substantially blocked. In other words, the optical filter is used to shield ambient light. Thus, an optical filter with a narrow passband in the near-infrared wavelength range, i.e. in the range of 800 nm to 1100 nm, is required. Furthermore, the optical filter must have a high level of light transmission in the passband and a high level of light blocking outside the passband.

[0005] Conventionally, the optical filter comprises a light filtering stack and a light blocking stack coated on opposite surfaces of a substrate. Each stack is formed of alternating stacks of high refractive index layers and low refractive index layers. The high refractive index layers and the low refractive index layers are typically formed of different oxides, such as Ti02, Nb205, Ta205, Si02, and mixtures thereof. For example, some conventional optical filters comprise a Ti02 / Si02light filtering stack and a Ta205 / Si02light blocking stack, wherein the high refractive index layers are composed of Ti02or Ta205, respectively, and the low refractive index layers are composed of Si02.

[0006] In a first conventional optical filter designed to transmit light in the wavelength range of 829 nm to 859 nm at an incidence angle range of 0° to 30°, the light filtering stack comprises 71 layers and the light blocking stack comprises 140 layers, with a total coating thickness of about 24 μm. The transmission spectrum 100 of this optical filter at 0° incidence angle and the transmission spectrum 101 at 30° incidence angle are shown in Figure 1are plotted in FIGS. 2 and 3, respectively. In a second conventional filter designed to transmit light having a wavelength of 825 nm at an incident angle ranging from 0° to 20°, the filter stack includes 43 layers, the blocker stack includes 82 layers, and the total coating thickness is approximately 14 μm. The transmission spectrum 200 of this filter at 0° incident angle and the transmission spectrum 201 of this filter at 20° incident angle are plotted in FIGS. 2 and 3, respectively. Figure 2 are plotted in FIGS. 2 and 3, respectively. In a second conventional filter designed to transmit light having a wavelength of 825 nm at an incident angle ranging from 0° to 20°, the filter stack includes 43 layers, the blocker stack includes 82 layers, and the total coating thickness is approximately 14 μm. The transmission spectrum 200 of this filter at 0° incident angle and the transmission spectrum 201 of this filter at 20° incident angle are plotted in FIGS. 2 and 3, respectively. Figure 3 are plotted in FIGS. 2 and 3, respectively. In a second conventional filter designed to transmit light having a wavelength of 825 nm at an incident angle ranging from 0° to 20°, the filter stack includes 43 layers, the blocker stack includes 82 layers, and the total coating thickness is approximately 14 μm. The transmission spectrum 200 of this filter at 0° incident angle and the transmission spectrum 201 of this filter at 20° incident angle are plotted in FIGS. 2 and 3, respectively.

[0007] Reference is made to Figures 1-3 The first, second, and third conventional filters generally have a high level of transmission within the passband and a high level of blocking outside the passband. However, the center wavelength of the passband shifts significantly with changes in the incident angle. As a result, the passband must be relatively wide in order to accept light within the desired range of incident angles, increasing the amount of ambient light that is transmitted, and reducing the signal-to-noise ratio of the system employing these conventional filters. In addition, the large number of layers in the filter stack and the blocker stack increases the cost and coating time to produce these conventional filters. The large total coating thickness also makes it difficult to pattern these conventional filters using techniques such as photolithography.

[0008] To improve the performance of the filter in a gesture recognition system, it is desirable to reduce the number of layers, the total coating thickness, and the shift in the center wavelength with changes in the incident angle. One approach is to use a material having a higher refractive index than conventional oxides over the wavelength range of 800 nm to 1100 nm for the high refractive index layers. In addition to having a higher refractive index, the material must also have a low extinction coefficient over the wavelength range of 800 nm to 1100 nm to provide a high level of transmission within the passband.

[0009] The use of hydrogenated silicon (Si:H) in high refractive index layers in optical filters is disclosed by Lairson et al. in the article entitled "Reduced Angle-Shift Infrared Bandpass Filter Coatings" (SPIE Conference Proceedings, 2007, Vol. 6545, pp. 65451C-1 to 65451C-5) and by Gibbons et al. in the article entitled "Development and Implementation of a Hydrogenated a-Si Reactive Sputter Deposition Process" (Annual Technical Conference Proceedings, Vacuum Coating Association, 2007, Vol. 50, pp. 327-330). Lairson et al. disclose a hydrogenated silicon material having a refractive index of 3.2 at a wavelength of 1500 nm and an extinction coefficient of less than 0.001 at wavelengths greater than 1000 nm. Gibbons et al. disclose a hydrogenated silicon material generated by alternating current (AC) sputtering having a refractive index of 3.2 at a wavelength of 830 nm and an extinction coefficient of 0.0005 at a wavelength of 830 nm. However, these hydrogenated silicon materials do not have a suitably low extinction coefficient in the 800 nm to 1100 nm wavelength range. SUMMARY

[0010] Accordingly, the present invention relates to an optical filter having a passband at least partially overlapping the 800 nm to 1100 nm wavelength range, the optical filter comprising: an optical filter stack, the optical filter stack comprising: a plurality of hydrogenated silicon layers, each layer of the plurality of hydrogenated silicon layers having a refractive index greater than 3 in the 800 nm to 1100 nm wavelength range and an extinction coefficient less than 0.0005 in the 800 nm to 1100 nm wavelength range; and a plurality of low refractive index layers, each layer of the plurality of low refractive index layers having a refractive index less than 3 in the 800 nm to 1100 nm wavelength range, the plurality of low refractive index layers being stacked alternately with the plurality of hydrogenated silicon layers.

[0011] The present application also relates to a sensor system comprising: a light source, a filter and a sensor, wherein the light source emits light at an emission wavelength in a wavelength range of 800 nm to 1100 nm; the filter has a passband comprising the emission wavelength and at least partially overlapping with the wavelength range of 800 nm to 1100 nm, the filter is arranged to receive the emitted light for transmitting the emitted light while substantially blocking ambient light, the filter comprises: a filter stack, the filter stack comprises: a plurality of hydrogenated silicon layers, each layer of the plurality of hydrogenated silicon layers has a refractive index greater than 3 in the wavelength range of 800 nm to 1100 nm and an extinction coefficient less than 0.0005 in the wavelength range of 800 nm to 1100 nm; and a plurality of low refractive index layers, each layer of the plurality of low refractive index layers has a refractive index less than 3 in the wavelength range of 800 nm to 1100 nm, the plurality of low refractive index layers are stacked alternately with the plurality of hydrogenated silicon layers; and the sensor is arranged to receive the transmitted light after passing through the filter for detecting the emitted light. BRIEF DESCRIPTION OF DRAWINGS

[0012] The present application will be described in more detail with reference to the accompanying drawings, in which:

[0013] Figure 1 Transmission spectra of a first conventional filter at 0° and 30° incident angles;

[0014] Figure 2 Transmission spectra of a second conventional filter at 0° and 20° incident angles;

[0015] Figure 3 Transmission spectra of a third conventional filter at 0° and 24° incident angles;

[0016] Figure 4 Schematic diagram of a sputter deposition system;

[0017] Figure 5A Transmission spectra of 1500 nm thick silicon layers deposited with and without hydrogen;

[0018] Figure 5B Graph of the relationship between the absorption edge wavelength at 50% transmittance level and the hydrogen flow rate of a hydrogenated silicon (Si:H) layer before and after an annealing step;

[0019] Figure 5C Graph of the relationship between the refractive index at 800 nm to 1120 nm wavelength and the hydrogen flow rate of a hydrogenated silicon layer;

[0020] Figure 5D Graph of the relationship between the absorption coefficient at 800 nm to 880 nm wavelength and the hydrogen flow rate of a hydrogenated silicon layer;

[0021] Figure 6 schematic cross-section of a filter according to the present invention;

[0022] Figure 7A Table comparing the characteristics of the first conventional filter in Figure 1

[0023] Figure 7B Table listing the layer number, material and thickness of the anti- reflective (AR) coating of the first example filter;

[0024] Figure 7C Table listing the layer number, material and thickness of the filter stack of the first example filter;

[0025] Figure 7D Transmission spectra of the first example filter at 0° and 30° incidence angle;

[0026] Figure 7E Transmission spectra of a filter similar to the first example filter, but comprising a Si / SiO2 filter stack, at 0° and 30° incidence angle;

[0027] Figure 8A Table comparing the characteristics of the second conventional filter in Figure 2

[0028] Figure 8B Table listing the layer number, material and thickness of the filter stack of the second example filter;

[0029] Figure 8C Transmission spectra of the second example filter at 0° and 20° incidence angle;

[0030] Figure 8D Transmission spectra of a filter similar to the second example filter, but comprising a Si / SiO2 filter stack, at 0° and 20° incidence angle;

[0031] Figure 9A Table listing the layer number, material and thickness of the filter stack of the third example filter according to the present invention;

[0032] Figure 9B Transmission spectra of the third example filter at 0° and 40° incidence angle;

[0033] Figure 10 Block diagram of a sensor system according to the present invention.

[0034] Detailed description of the invention

[0035] ​​The present invention relates to optical filters and sensor systems comprising optical filters. More specifically, the present invention relates to optical filters comprising a layer of hydrogenated silicon and sensor systems comprising the optical filters.

[0036] In one embodiment, the present invention relates to a method of manufacturing an optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm, the method comprising:

[0037] forming a plurality of layers of hydrogenated silicon of the optical filter using pulsed direct current sputtering;

[0038] the plurality of layers of hydrogenated silicon having a first refractive index greater than 3 in an operational wavelength range of 800 nm to 1100 nm of the optical filter; and

[0039] the plurality of layers of hydrogenated silicon being formed in a deposition chamber; and

[0040] forming a plurality of low refractive index layers of the optical filter;

[0041] each layer of the plurality of low refractive index layers having a second refractive index less than 3 in the operational wavelength range of 800 nm to 1100 nm of the optical filter;

[0042] the plurality of low refractive index layers being alternately stacked with the plurality of layers of hydrogenated silicon; and

[0043] wherein the plurality of layers of hydrogenated silicon has an extinction coefficient less than 0.0005 in the wavelength range of 800 nm to 1100 nm.

[0044] In one embodiment, the present invention relates to a method of manufacturing an optical filter, wherein forming the plurality of layers of hydrogenated silicon comprises:

[0045] sputtering silicon to deposit the plurality of layers of hydrogenated silicon onto a substrate.

[0046] In one embodiment, the present invention relates to a method of manufacturing an optical filter, wherein sputtering silicon comprises:

[0047] sputtering silicon using a cathode having a silicon target.

[0048] In one embodiment, the present invention relates to a method of manufacturing an optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm and having a transmittance greater than 90% in the passband.

[0049] In one embodiment, the present invention relates to a method of manufacturing an optical filter, wherein the plurality of layers of hydrogenated silicon and the plurality of low refractive index layers are a multilayer structure; and

[0050] the method further comprising:

[0051] annealing the multilayer structure at a temperature between 250 degrees Celsius and 350 degrees Celsius.

[0052] In one embodiment, the present invention relates to a method of manufacturing an optical filter, wherein the plurality of hydrogenated silicon layers and the plurality of low refractive index layers are a multilayer structure; and

[0053] The method further comprises:

[0054] annealing the multilayer structure for 30 minutes to 90 minutes.

[0055] In one embodiment, the present invention relates to a method of manufacturing an optical filter, further comprising:

[0056] providing a hydrogen plasma into the deposition chamber using a plasma excitation source.

[0057] In one embodiment, the present invention relates to a method of manufacturing an optical filter, wherein the plurality of hydrogenated silicon layers and the plurality of low refractive index layers are a multilayer structure; and

[0058] The method further comprises:

[0059] forming the multilayer structure on a charge-coupled device (CCD) chip or a complementary metal-oxide-semiconductor (CMOS) chip using wafer-level processing techniques.

[0060] In one embodiment, the present invention relates to a method of manufacturing an optical filter, wherein forming the plurality of hydrogenated silicon layers comprises:

[0061] forming the plurality of hydrogenated silicon layers at a deposition rate between 0.05 nm / s and 1.2 nm / s.

[0062] In one embodiment, the present invention relates to a method of manufacturing an optical filter, wherein forming the plurality of hydrogenated silicon layers comprises:

[0063] forming the plurality of hydrogenated silicon layers at a deposition rate between 0.8 nm / s and 1.2 nm / s.

[0064] In one embodiment, the present invention relates to a method of manufacturing an optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm, comprising:

[0065] manufacturing the plurality of hydrogenated silicon (Si:H) layers of the multilayer structure of the optical filter using pulsed direct current sputtering techniques;

[0066] The plurality of hydrogenated silicon (Si:H) layers are manufactured in a vacuum deposition chamber; and

[0067] the plurality of silicon hydride (Si:H) layers have a first refractive index greater than 3 in a wavelength range of 800 nm to 1100 nm; and

[0068] manufacturing a plurality of low refractive index layers;

[0069] the plurality of low refractive index layers have a second refractive index less than 3 in a wavelength range of 800 nm to 1100 nm;

[0070] the plurality of low refractive index layers are alternately stacked with the plurality of silicon hydride (Si:H) layers; and

[0071] wherein the plurality of silicon hydride (Si:H) layers have an extinction coefficient less than 0.0005 in a wavelength range of 800 nm to 1100 nm.

[0072] In one embodiment, the present invention relates to a method of manufacturing an optical filter, further comprising:

[0073] annealing the multi-layer structure of the optical filter at a temperature between 250 degrees Celsius to 350 degrees Celsius.

[0074] In one embodiment, the present invention relates to a method of manufacturing an optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm and having a transmittance greater than 90% within the passband.

[0075] In one embodiment, the present invention relates to an optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm, comprising:

[0076] a plurality of silicon hydride layers, wherein the plurality of silicon hydride layers have a refractive index greater than 3;

[0077] a plurality of low refractive index layers, wherein the plurality of low refractive index layers comprise at least one oxide other than silicon dioxide;

[0078] wherein the plurality of low refractive index layers comprise at least one of aluminum oxide (AI2O3), titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), or a mixture thereof; and

[0079] wherein the plurality of silicon hydride (Si:H) layers have an extinction coefficient less than 0.0005 in a wavelength range of 800 nm to 1100 nm, and a center wavelength of the passband shifts in magnitude less than 20 nm as an incident angle changes from 0° to 30°.

[0080] In one embodiment, the present application is directed to an optical filter, wherein the center wavelength of the passband is about 850 nm at 0° angle of incidence, and the center wavelength of the passband shifts in magnitude by about 12.2 nm as the angle of incidence changes from 0° to 30°.

[0081] In one embodiment, the present application is directed to an optical filter, wherein the optical filter has an optical density greater than OD2 over a wavelength range of 400 nm to 1100 nm.

[0082] In one embodiment, the present application is directed to an optical filter, wherein the optical filter has an optical density greater than OD3 over a wavelength range of 300 nm to 1100 nm.

[0083] In one embodiment, the present application is directed to an optical filter, wherein the plurality of hydrogenated silicon layers have a refractive index greater than 3.6 at a wavelength of 830 nm.

[0084] In one embodiment, the present application is directed to an optical filter, wherein the top layer of the optical filter is one of the plurality of low refractive index layers.

[0085] In one embodiment, the present application is directed to an optical filter, wherein the optical filter has a transmittance greater than 90% over a passband.

[0086] In one embodiment, the present application is directed to an optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm, comprising:

[0087] a plurality of hydrogenated silicon layers, wherein the plurality of hydrogenated silicon layers have a refractive index greater than 3 over a wavelength range of 800 nm to 1100 nm; a plurality of low refractive index layers, wherein each of the plurality of low refractive index layers has a refractive index less than 3 over a wavelength range of 800 nm to 1100 nm, wherein the plurality of low refractive index layers are stacked in an alternating stack with the plurality of hydrogenated silicon (Si:H) layers, and the plurality of hydrogenated silicon layers have an extinction coefficient less than 0.0005 over a wavelength range of 800 nm to 1100 nm.

[0088] In one embodiment, the present application is directed to an optical filter, wherein the optical filter has a transmittance greater than 90% over a passband.

[0089] In one embodiment, the present application is directed to an optical filter, wherein the plurality of low refractive index layers comprise at least one oxide.

[0090] In one embodiment, the present application relates to an optical filter, wherein the plurality of low refractive index layers comprises at least one of silicon dioxide (Si02), aluminum oxide (AI2O3), titanium dioxide (Ti02), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), or mixtures thereof.

[0091] In one embodiment, the present application relates to an optical filter, wherein the total coating thickness of the optical filter is less than 10 pm.

[0092] In one embodiment, the present application relates to an optical filter, wherein the optical filter has a passband, a center wavelength of the passband shifts in magnitude by less than 20 nm as a function of change in angle of incidence from 0° to 30°.

[0093] In one embodiment, the present application relates to an optical filter, wherein at 0° angle of incidence, a center wavelength of the passband is about 850 nm, and a center wavelength of the passband shifts in magnitude by about 12.2 nm as a function of change in angle of incidence from 0° to 30°.

[0094] In one embodiment, the present application relates to an optical filter, wherein the plurality of hydrogenated silicon layers has a refractive index greater than 3.6 at a wavelength of 830 nm.

[0095] In one embodiment, the present application relates to an optical filter, wherein a top layer of the optical filter is one of the plurality of low refractive index layers.

[0096] In one embodiment, the present application relates to an optical filter, wherein the optical filter is a narrow bandpass filter, and a center wavelength of the passband is in a wavelength range of 800 nm to 1100 nm.

[0097] In one embodiment, the present application relates to an optical filter, wherein the passband has a full width at half maximum (FWHM) of less than 50 nm.

[0098] In one embodiment, the present application relates to an optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm, comprising:

[0099] a first optical filter stack on a first side of the substrate, the first optical filter stack comprising alternating layers of hydrogenated silicon and low refractive index material; and

[0100] an anti-reflective coating on an opposing second side of the substrate;

[0101] wherein the hydrogenated silicon layer has a refractive index greater than 3 in the operating wavelength range of the optical filter of 800 nm to 1100 nm, each of the low refractive index material layers has a second refractive index less than 3 in the operating wavelength range of the optical filter of 800 nm to 1100 nm, and the plurality of hydrogenated silicon layers has an extinction coefficient less than 0.0005 in the wavelength range of 800 nm to 1100 nm.

[0102] In one embodiment, the present application relates to an optical filter, wherein the optical filter has a passband, a center wavelength of the passband is about 850 nm at 0° angle of incidence, and the center wavelength of the passband shifts in magnitude by less than 20 nm as the angle of incidence varies from 0° to 30°.

[0103] In one embodiment, the present application relates to an optical filter, wherein the optical filter has a passband, a center wavelength of the passband is about 850 nm at 0° angle of incidence, and the center wavelength of the passband shifts in magnitude by about 12.2 nm as the angle of incidence varies from 0° to 30°.

[0104] In one embodiment, the present application relates to an optical filter, wherein the optical filter has an optical density greater than OD2 in a wavelength range of 400 nm to 1100 nm.

[0105] In one embodiment, the present application relates to an optical filter, wherein the optical filter has an optical density greater than OD3 in a wavelength range of 300 nm to 1100 nm.

[0106] In one embodiment, the present application relates to an optical filter, wherein the low refractive index layer material has a refractive index less than 2.5 in a wavelength range of 800 nm to 1100 nm.

[0107] In one embodiment, the present application relates to an optical filter, wherein the anti-reflective coating comprises silicon dioxide (Si02) and tantalum pentoxide (Ta205).

[0108] In one embodiment, the present application relates to an optical filter, wherein the coating has a thickness of 0.1 um to 1 um.

[0109] In one embodiment, the present application relates to an optical filter, wherein the total coating thickness of the optical filter is less than 10 um.

[0110] In one embodiment, the present application relates to an optical filter, wherein the hydrogenated silicon layer has a refractive index greater than 3.6 at a wavelength of 830 nm.

[0111] In one embodiment, the present application relates to an optical filter, wherein the optical filter is a narrow passband filter, and a center wavelength of the passband is in a wavelength range of 800 nm to 1100 nm.

[0112] In one embodiment, the present application is directed to an optical filter, wherein the passband has a full width at half maximum (FWHM) of less than 50 nm.

[0113] In one embodiment, the present application is directed to an optical filter having a transmittance of greater than 90% in the passband.

[0114] In one embodiment, the present application is directed to an optical filter, wherein the top layer of the first optical filter stack is a layer of low refractive index material.

[0115] The present application provides an optical filter including a layer of hydrogenated silicon (Si:H) that is particularly suitable for use in sensor systems such as distance sensor systems, three-dimensional (3D) imaging systems, or gesture recognition systems.

[0116] The optical filter of the present application employs an improved hydrogenated silicon material that has both a relatively high refractive index and a relatively low absorption coefficient in the wavelength range of 800 nm to 1100 nm, i.e., in the near infrared wavelength range. Typically, the hydrogenated silicon material is amorphous. The hydrogenated silicon material is preferably produced using a pulsed direct current (DC) sputtering method. A sputter deposition system suitable for producing the hydrogenated silicon material is described in U.S. Patent No. 8,163,144 to Tilsch et al., issued April 24, 2012, which is incorporated herein by reference.

[0117] Referring to Figure 4 A typical sputter deposition system 400 for producing the hydrogenated silicon material includes a vacuum chamber 410, a substrate 420, a cathode 430, a cathode power supply 440, an anode 450, a plasma activation source (PAS) 460, and a PAS power supply 470. The cathode 430 is powered by the cathode power supply 440, which is a pulsed direct current power supply. The PAS 460 is powered by the PAS power supply 470, which is a radio frequency (RF) power supply.

[0118] The cathode 430 includes a silicon target 431 that is sputtered in the presence of hydrogen gas (H2) and an inert gas, such as argon, to deposit a layer of hydrogenated silicon material on the substrate 420. The inert gas is introduced into the vacuum chamber 410 through the anode 450 and the PAS 460. Alternatively, the chamber walls of the vacuum chamber 410 can serve as the anode, and the inert gas can be introduced at a different location.

[0119] Hydrogen is introduced into the vacuum chamber 410 through a PAS 460 which is used to activate the hydrogen. Active hydrogen is more chemically active and therefore more likely to generate Si-H bonds which are believed to determine the optical properties of the hydrogenated silicon material. The PAS 460 is located very close to the cathode 430 so that the PAS plasma and the cathode plasma overlap. Both atomic and molecular forms of active hydrogen are believed to exist in the plasma. The use of a PAS 460 allows the deposition of a hydrogenated silicon layer at a relatively high deposition rate and with a relatively low hydrogen content. Typically, the deposition rate of the hydrogenated silicon layer is between 0.05 nm / s and 1.2 nm / s, preferably about 0.8 nm / s. Alternatively, the hydrogen activation can be performed using a cathode plasma alone.

[0120] The optical properties of the hydrogenated silicon material are mainly determined by the hydrogen content in the vacuum chamber 410 and therefore by the hydrogen flow. However, they are also influenced by other parameters such as the flow of inert gas, the PAS power level, the cathode power level and the deposition rate.

[0121] Figure 5A Transmission spectra 500 and 501 of 1500 nm thick silicon layers deposited with hydrogen, at a hydrogen flow of 139 seem, and without hydrogen, respectively, are shown. The silicon layer deposited with hydrogen, i.e. the hydrogenated silicon layer, has a significantly higher level of transmission in the wavelength range from 800 nm to 1100 nm.

[0122] Figure 5B The relationship between the absorption edge wavelength at 50% transmission and the hydrogen flow is shown for the hydrogenated silicon layer before the annealing step and after the annealing step, respectively, in curves 510 and 511. For the deposited hydrogenated silicon layer, the absorption edge wavelength decreases with increasing hydrogen flow. In general, the absorption edge wavelength varies approximately logarithmically with the hydrogen flow. The absorption edge wavelength is further decreased by the annealing step which is performed at a temperature of about 300°C for about 60 minutes. Typically, when the optional post-coating annealing step is performed, the hydrogenated silicon layer is annealed at a temperature of up to 350°C for up to 120 minutes, preferably at a temperature of 250°C to 350°C for 30 to 90 minutes. In some cases, more than one annealing step can be performed.

[0123] Thus, the absorption edge wavelength of the hydrogenated silicon material can be adjusted by adjusting the hydrogen flow and optionally by annealing. Likewise, the refractive index and the absorption coefficient of the hydrogenated silicon material can be adjusted by adjusting the hydrogen flow and optionally by annealing. Typically, a hydrogen flow of more than 80 seem is used for the deposition of the hydrogenated silicon layer, preferably a hydrogen flow of about 80 seem. However, it should be noted that the hydrogen content associated with this flow will depend on the pumping speed of the vacuum system.

[0124] Figure 5CA plot showing the refractive index of the deposited silicon hydride layer versus hydrogen flow rate at wavelengths from 800 nm to 1120 nm is shown. The refractive index decreases with increasing hydrogen flow rate. In general, the refractive index varies approximately linearly with hydrogen flow rate. Specifically, the refractive index of the silicon hydride layer generated at a hydrogen flow rate of 80 seem is greater than 3.55 over the wavelength range from 800 nm to 1120 nm.

[0125] Figure 5D A plot showing the absorption coefficient of the deposited silicon hydride layer versus hydrogen flow rate at wavelengths from 800 nm to 880 nm (the absorption coefficient is less than 0.0001 at wavelengths from 920 nm to 1120 nm) is shown. The absorption coefficient decreases with increasing hydrogen flow rate. In general, the absorption coefficient varies approximately exponentially with hydrogen flow rate. Specifically, the absorption coefficient of the silicon hydride layer generated at a hydrogen flow rate of 80 seem is less than 0.0004 over the wavelength range from 800 nm to 1120 nm.

[0126] The improved silicon hydride material is employed in the optical filter of the present application, which is tailored to have suitable optical properties. Referring to Figure 6 , the optical filter 600 includes an optical filter stack 610 disposed on a first surface of a substrate 620. In most cases, the substrate 620 is a self-supporting substrate, typically a glass substrate, such as a float-boron-silicate glass substrate. Alternatively, the substrate 620 can be a sensor or other device. When the substrate 620 is a self-supporting substrate, an anti-reflective (AR) coating 630 is often disposed on a second surface of the substrate 620 opposite the first surface. Typically, the AR coating 630 is a multilayer interference coating, such as a Ta2O 5 / SiO2coating. Also in typical cases, the AR coating 630 has a thickness of 0.1 μm to 1 μm.

[0127] The optical filter stack 610 includes a plurality of silicon hydride layers 611 serving as high refractive index layers, and a plurality of low refractive index layers 612, the plurality of silicon hydride layers being stacked alternately with the plurality of low refractive index layers. Typically, the optical filter stack 610 includes a plurality of silicon hydride layers 611 and a plurality of low refractive index layers 612 stacked in the order (high / low) n , (high / low) n (high / low) n . Typically, the optical filter stack 610 includes a total of 10 to 100 layers, i.e., 5 < n < 50. Also in typical cases, each of the silicon hydride layers 611 and the low refractive index layers 612 has a thickness of 3 nm to 300 nm, and the optical filter stack 610 has a thickness of 1 μm to 10 μm. In general, the number of layers and the thickness are selected according to the specific optical design. Preferably, the total coating thickness of the optical filter 600, i.e., the total thickness of the optical filter stack 610 and the AR coating 630, is less than 10 μm.

[0128] The hydrogenated silicon layer 611 is composed of an improved hydrogenated silicon material that is tailored to have a refractive index greater than 3 and an extinction coefficient less than 0.0005 in the wavelength range of 800 nm to 1100 nm. Preferably, the hydrogenated silicon material has a refractive index greater than 3.5 in the wavelength range of 800 nm to 1100 nm, for example, a refractive index greater than 3.64, i.e., about 3.6, at a wavelength of 830 nm. Generally, a higher refractive index is more desirable. However, in general, the hydrogenated silicon material has a refractive index less than 4.5 in the wavelength range of 800 nm to 1100 nm.

[0129] Preferably, the hydrogenated silicon material has an extinction coefficient less than 0.0004 in the wavelength range of 800 nm to 1100 nm, and more preferably, an extinction coefficient less than 0.0003 in the wavelength range of 800 nm to 1100 nm. Generally, the hydrogenated silicon material has an extinction coefficient greater than 0.01 at a wavelength less than 600 nm, and preferably, an extinction coefficient greater than 0.05 at a wavelength less than 650 nm. Because the hydrogenated silicon material has relatively strong light absorption at a wavelength less than 600 nm, no additional light blocking layers are needed in the optical filter 600.

[0130] The low refractive index layer 612 is composed of a low refractive index material that has a refractive index lower than that of the hydrogenated silicon layer 611 in the wavelength range of 800 nm to 1100 nm. Generally, the low refractive index material has a refractive index less than 3 in the wavelength range of 800 nm to 1100 nm. Preferably, the low refractive index material has a refractive index less than 2.5 in the wavelength range of 800 nm to 1100 nm, and more preferably, a refractive index less than 2 in the wavelength range of 800 nm to 1100 nm.

[0131] It is generally desirable for the low refractive index layer 612 to have a low refractive index to increase the width of the wavelength range (i.e., the stop band) that the optical filter 600 blocks light, so that the same level of light blocking can be achieved with fewer layers in the optical filter stack 610. However, in some cases, a slightly higher, but still lower refractive index than that of the hydrogenated silicon layer 611 can be desirable to reduce the shift in the center wavelength of the optical filter 600 with the change in the angle of incidence (i.e., the angular shift).

[0132] In most cases, the low refractive index material is a dielectric material, typically an oxide. Suitable low refractive index materials include silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), and mixtures thereof, i.e., mixed oxides.

[0133] The optical filter 600 can be fabricated using a sputtering process. Typically, the layers are deposited in the order of Figure 4A substrate 620 is provided in the vacuum chamber of a similar sputter deposition system as shown. A silicon hydride layer 611 and a low refractive index layer 612 are then sequentially deposited on a first surface of the substrate 620 to form the optical filter stack 610 as a multilayer coating. Typically, the silicon hydride layer 611 is deposited by pulsed DC sputtering of a silicon target in the presence of hydrogen, as described above. Also typically, the low refractive index layer 612 is deposited by pulsed DC sputtering of one or more suitable metal targets (e.g., silicon, aluminum, titanium, niobium, and / or tantalum) in the presence of oxygen. The AR coating 630 is deposited on a second surface of the substrate 620 in a similar manner. It should be noted that the order in which the optical filter stack 610 and the AR coating 630 are formed is generally not important.

[0134] The optical filter 600 is an interference filter having a passband that at least partially overlaps the wavelength range from 800 nm to 1100 nm. The passband can include the entire wavelength range from 800 nm to 1100 nm, or more typically, only a portion of the wavelength range. The passband can be limited to a portion or all of the wavelength range from 800 nm to 1100 nm, or can extend beyond this wavelength range. Preferably, the optical filter 600 has a transmittance greater than 90% in the passband, in the wavelength range from 800 nm to 1100 nm.

[0135] The optical filter 600 provides a blocking function outside the passband, i.e., has a stopband on one or both sides of the passband, typically in the wavelength range from 400 nm to 1100 nm, and preferably in the wavelength range from 300 nm to 1100 nm. Preferably, the optical filter 600 has a blockage greater than OD2 in the wavelength range from 400 nm to 1100 nm, and more preferably, a blockage greater than OD3 in the wavelength range from 300 nm to 1100 nm, outside the passband.

[0136] In some cases, the optical filter 600 is a long-wavelength pass filter, having a cutoff wavelength in the wavelength range from 800 nm to 1100 nm. However, in most cases, the optical filter 600 is a bandpass filter, and preferably a narrow bandpass filter. Typically, the center wavelength of the passband is in the wavelength range from 800 nm to 1100 nm. Preferably, the full width at half maximum (FWHM) of the passband is less than 50 nm. Often, the entire passband is in the wavelength range from 800 nm to 1100 nm.

[0137] In general, the center wavelength of the optical filter 600 shifts slightly with changes in the angle of incidence. Preferably, the center wavelength of the passband shifts by less than 20 nm when the angle of incidence is changed from 0° to 30°. Thus, the optical filter 600 has a wide acceptance angle.

[0138] The optical filter 600 can employ a variety of optical designs. In general, the optical design of the optical filter 600 can achieve the best design for a filter of a particular passband by selecting appropriate numbers of layers, materials, and / or thicknesses for the filter stack 610. Some example filters described below include Si:H / SiO2 filter stacks and Ta2O5 / SiO2 AR coatings applied to opposite sides of a float glass borosilicate substrate.

[0139] Referring to FIG. 7, a first example filter is a narrow bandpass filter designed to transmit light in the wavelength range of 829 nm to 859 nm over the range of 0° to 30° incident angles. The first example filter in FIG. 7 is comparable to the first conventional filter in FIG. 6, Figure 1 Figure 7A Some characteristics of the two filters are compared. Figure 7B 7C Design data for the AR coating and filter stack of the first example filter are listed in Tables 1 and 2, respectively, namely the number of layers (from substrate to air), the material, and the thickness of the layers. The filter stack includes 48 layers and the AR coating includes 5 layers, for a total coating thickness of about 5.7 μιη.

[0140] The transmission spectrum 700 of the first example filter at 0° incident angle and the transmission spectrum 701 of the first example filter at 30° incident angle are plotted in FIG. 7. The first example filter has a transmittance of greater than 90% in the passband and an optical density of greater than OD3 in the wavelength range of 450 nm to 1050 nm outside the passband. At 0° incident angle, the center wavelength of the passband is about 850 nm and the FWHM is about 46.5 nm. The center wavelength of the passband shifts by about -12.2 nm as the incident angle changes from 0° to 30°. Figure 7D Advantageously, the first example filter in FIG. 7 includes a smaller number of layers and a smaller total coating thickness than the first conventional filter in FIG. 6. In particular, the total coating thickness of the first example filter is about ¼ of the total coating thickness of the first conventional filter. As a result, the first example filter is less expensive to manufacture and is easier to pattern. It is also advantageous that the first example filter has a smaller shift in center wavelength with incident angle. As a result, the passband of the first example filter can be substantially narrower while still accepting light over the same range of incident angles, improving the signal-to-noise ratio of a system employing the first example filter.

[0141] Figure 1 The first example filter can also be compared to a similar filter including a Si / SiO2 filter stack (i.e., a filter stack including non-hydrogenated silicon layers) instead of a Si:H / SiO2 filter stack. The transmission spectrum 710 of the filter at 0° incident angle and the transmission spectrum 711 of the filter at 30° incident angle are plotted in FIG. 8. The filter has a transmittance of greater than 90% in the wavelength range of 829 nm to 859 nm over the range of 0° to 30° incident angles. At 0° incident angle, the center wavelength of the passband is about 840 nm and the FWHM is about 48.5 nm. The center wavelength of the passband shifts by about -12.2 nm as the incident angle changes from 0° to 30°.

[0142] The first example filter can also be compared to a similar filter including a Si / SiO2 filter stack (i.e., a filter stack including non-hydrogenated silicon layers) instead of a Si:H / SiO2 filter stack. The transmission spectrum 710 of the filter at 0° incident angle and the transmission spectrum 711 of the filter at 30° incident angle are plotted in FIG. 8. The filter has a transmittance of greater than 90% in the wavelength range of 829 nm to 859 nm over the range of 0° to 30° incident angles. At 0° incident angle, the center wavelength of the passband is about 840 nm and the FWHM is about 48.5 nm. The center wavelength of the passband shifts by about -12.2 nm as the incident angle changes from 0° to 30°.​​​Figure 7E The following diagrams are drawn separately. This filter has extremely low transmittance within its passband and is therefore unusable.

[0143] Referring to Figure 8, the second example filter is a narrower bandpass filter designed to transmit light with a wavelength of 825 nm over an incident angle range of 0° to 20°. The second example filter in Figure 8 is similar to... Figure 2 The second type of conventional filter is equivalent to, Figure 8A Some characteristics of the two filters were compared. The design data for the AR coating of the second example filter was the same as that of the first example filter, both within... Figure 7B The design data for the filter stack of the second example filter is listed in [the table / document]. Figure 8B Listed in the document. The filter stack consists of 25 layers, the AR coating consists of 5 layers, and the total coating thickness is approximately 3.3 μm.

[0144] The second example filter has a transmission spectrum 800 at an incident angle of 0° and a transmission spectrum 801 at an incident angle of 20°. Figure 8C The images are drawn separately. The second example filter has a transmittance of over 90% within the passband and an opacity higher than OD2 in the wavelength range of 400 nm to 1100 nm outside the passband. At a 0° incident angle, the center wavelength of the passband is approximately 829 nm, and the FWHM is approximately 29.6 nm. When the incident angle changes from 0° to 20°, the center wavelength of the passband shifts by approximately -7.8 nm.

[0145] Similar to the first example filter in Figure 7, the second example filter in Figure 8 has the advantage of including fewer layers, a smaller total coating thickness, and a smaller shift in center wavelength with the incident angle compared to... Figure 2 The second type of conventional filter has a small offset.

[0146] The second example filter can also be compared with similar filters that include a Si / SiO2 filter stack rather than a Si:H / SiO2 filter stack. The transmission spectrum 810 of this filter at a 0° incident angle and the transmission spectrum 811 at a 20° incident angle are... Figure 8D The following diagrams are drawn separately. This filter has extremely low transmittance within its passband and is therefore unusable.

[0147] Referring to Figure 9, the third example filter is a narrow bandpass filter, designed to transmit light in the wavelength range of 845 nm to 865 nm within an incident angle range of 0° to 40°. The third example filter in Figure 9... Figure 3 The third type of conventional filter is similar. The design data for the AR coating of the third example filter is the same as that of the first example filter, both being in... Figure 7B The design data for the filter stack of the third example filter is listed in [the table / document]. Figure 9AThe filter stack includes 29 layers, the AR coating includes 5 layers, and the total coating thickness is about 4.8 μm.

[0148] The transmission spectrum 900 of the third example filter at 0° incidence and the transmission spectrum 901 of the third example filter at 40° incidence are plotted in Figure 9B FIG. 9. The passband width of the third example filter in FIG. 9 is substantially the same as the passband width of the third conventional filter in Figure 3 FIG. 9, but the transmittance within the passband of the third example filter is slightly lower. Advantageously, however, the third example filter accepts a much larger range of incident angles of light (0° to 40°) than the third conventional filter, which accepts a range of incident angles of light of only 0° to 24°. In other words, the third example filter has a significantly wider range of acceptance of incident angles. Also advantageously, the third example filter includes fewer layers and has a smaller total coating thickness, which is only about 1 / 5 of the total coating thickness of the third conventional filter.

[0149] As mentioned previously, the filters of the present application are particularly useful when forming part of a sensor system, such as a distance sensor system, a three- dimensional imaging system, or a gesture recognition system. See, for example, Figure 10 FIG. 10, which illustrates a typical sensor system 1000 that includes a light source 1010, a filter 1020 according to the present application, and a sensor 1030. Note that other elements typically included in a sensor system, such as optical elements, are omitted here for simplicity of illustration.

[0150] The light source 1010 emits light at an emission wavelength in the wavelength range of 800 nm to 1100 nm. Typically, the light source 1010 emits modulated light, such as pulses of light. Preferably, the light source 1010 is a light emitting diode (LED), an array of LEDs, a laser diode, or an array of laser diodes. The light source 1010 emits light toward a target 1040, which reflects the emitted light back toward the sensor system 1000. When the sensor system 1000 is a gesture recognition system, the target 1040 is a user of the gesture recognition system.

[0151] The filter 1020 is positioned to receive the emitted light after it is reflected by the target 1040. The passband of the filter 1020 includes the emission wavelength and at least partially overlaps the wavelength range of 800 nm to 1100 nm. Typically, the filter 1020 is a bandpass filter, and preferably a narrow bandpass filter as described previously. The filter 1020 transmits the light emitted from the light source 1010 while substantially blocking ambient light. In short, the filter 1020 receives the light emitted by the light source 1010 and reflected by the target 1040 and transmits the emitted light to the sensor 1030.

[0152] The sensor 1030 is disposed to receive the emitted light transmitted through the optical filter 1020, i.e., the sensor 1030 is disposed behind the optical filter 1020. In some cases, the optical filter 1020 is formed directly on the sensor 1030, thereby being disposed on the sensor 1030. For example, in wafer level processing (WLP), the optical filter 1020 can be coated and patterned on the sensor, such as a distance sensor, by photolithography or the like.

[0153] When the sensor system 1000 is a distance sensor system, the sensor 1030 is a distance sensor that detects the emitted light to sense the distance of the target 1040 according to methods known in the art. When the sensor system 1000 is a three-dimensional imaging system or a gesture recognition system, the sensor 1030 is a three-dimensional image sensor, such as a charge-coupled device (CCD) chip or a complementary metal-oxide-semiconductor (CMOS) chip, that detects the emitted light to provide a three-dimensional image of the target 1040, which in some cases is a user. Typically, the three-dimensional image sensor converts optical information into electrical signals for processing by a processing system, such as an application specific integrated circuit (ASIC) chip or a digital signal processor (DSP) chip, according to methods known in the art. For example, when the sensor system 1000 is a gesture recognition system, the processing system processes the three-dimensional image of the user to recognize a gesture of the user.

Claims

1. A narrow-band optical filter having a passband at least partially overlapping a wavelength range of 800 nm to 1100 nm, comprising: an optical filter stack disposed on a first surface of a substrate and an anti-reflective coating disposed on a second surface opposite the first surface, wherein the optical filter stack comprises: a plurality of hydrogenated silicon layers, wherein each layer of the plurality of hydrogenated silicon layers has a refractive index greater than 3 in the wavelength range of 800 nm to 1100 nm; and a plurality of low refractive index layers, wherein each layer of the plurality of low refractive index layers has a refractive index less than 3 in the wavelength range of 800 nm to 1100 nm, wherein the plurality of low refractive index layers are stacked in an alternating stack with the plurality of hydrogenated silicon (Si:H) layers, and each layer of the plurality of hydrogenated silicon layers has an extinction coefficient less than 0.0005 in the wavelength range of 800 nm to 1100 nm, wherein a center wavelength of the passband is in the wavelength range of 800 nm to 1100 nm and shifts in magnitude by less than 20 nm as a function of a change in an angle of incidence from 0° to 30°, and wherein the optical filter has a transmittance greater than 90% within the passband.

2. The optical filter of claim 1, wherein each layer of the plurality of hydrogenated silicon layers has an extinction coefficient less than 0.0004 in the wavelength range of 800 nm to 1100 nm.

3. The optical filter of claim 1, wherein the plurality of low refractive index layers comprises at least one oxide.

4. The optical filter of claim 1, wherein the plurality of low refractive index layers comprises at least one of silicon dioxide (SiO2), aluminum oxide (Al2O3), titanium dioxide (TiO2), niobium pentoxide (Nb2O5), tantalum pentoxide (Ta2O5), or a mixture thereof.

5. The optical filter of claim 1, wherein a total coating thickness of the optical filter is less than 10 pm.

6. The optical filter of claim 1, wherein an operational wavelength range of the optical filter is 800 nm to 1100 nm.

7. The optical filter of claim 1, wherein a center wavelength of the passband is 850 nm at a 0° angle of incidence and the center wavelength of the passband shifts in magnitude by 12.2 nm as a function of a change in the angle of incidence from 0° to 30°.

8. The optical filter of claim 1, wherein the plurality of hydrogenated silicon layers has a refractive index greater than 3.6 at a wavelength of 830 nm.

9. The optical filter of claim 1, wherein a top layer of the optical filter is one of the plurality of low refractive index layers.

10. The optical filter of claim 1, wherein each layer of the plurality of hydrogenated silicon layers has a refractive index greater than 3.5 in the wavelength range of 800 nm to 1100 nm.

11. The optical filter of claim 1, wherein the passband has a full width at half maximum (FWHM) of less than 50 nm.

12. The optical filter of claim 1, wherein each layer of the plurality of hydrogenated silicon layers has a refractive index less than 4.5 in the wavelength range of 800 nm to 1100 nm.

13. The optical filter of claim 1, wherein each layer of the plurality of hydrogenated silicon layers has an extinction coefficient at wavelengths less than 600 nm that is greater than 0.

01.

14. The optical filter of claim 1, wherein each layer of the plurality of hydrogenated silicon layers has an extinction coefficient at wavelengths less than 650 nm that is greater than 0.

05.

15. The optical filter of claim 1, wherein each layer of the plurality of low refractive index layers has a refractive index in the wavelength range of 800 nm to 1100 nm that is less than 3.

16. The optical filter of claim 1, wherein each layer of the plurality of low refractive index layers has a refractive index in the wavelength range of 800 nm to 1100 nm that is less than 2.

5.

17. The optical filter of claim 1, wherein each layer of the plurality of low refractive index layers has a refractive index in the wavelength range of 800 nm to 1100 nm that is less than 2.

18. A method of manufacturing the optical filter of one of claims 1-17, comprising: forming the plurality of hydrogenated silicon layers of the optical filter using a pulsed direct current sputtering technique; and forming the plurality of hydrogenated silicon layers in a deposition chamber; and forming the plurality of low refractive index layers of the optical filter.

19. The method of claim 18, wherein forming the plurality of hydrogenated silicon layers comprises: sputtering silicon to deposit the plurality of hydrogenated silicon layers onto a substrate.

20. The method of claim 19, wherein sputtering silicon comprises: sputtering silicon using a cathode having a silicon target.

21. The method of claim 18, wherein the plurality of hydrogenated silicon layers and the plurality of low refractive index layers are a multilayer structure; and the method further comprising: annealing the multilayer structure at a temperature between 250 degrees Celsius and 350 degrees Celsius.

22. The method of claim 18, wherein the plurality of hydrogenated silicon layers and the plurality of low refractive index layers are a multilayer structure; and the method further comprising: annealing the multilayer structure for between 30 minutes and 90 minutes.

23. The method of claim 18, further comprising: providing a hydrogen plasma into the deposition chamber using a plasma excitation source.

24. The method of claim 18, wherein the plurality of hydrogenated silicon layers and the plurality of low refractive index layers are a multilayer structure; and the method further comprising: forming the multilayer structure on a charge-coupled device (CCD) chip or a complementary metal-oxide-semiconductor (CMOS) chip using wafer-level processing techniques.

25. The method of claim 18, wherein forming the plurality of hydrogenated silicon layers comprises: forming the plurality of hydrogenated silicon layers at a deposition rate between 0.05 nm / s and 1.2 nm / s.

26. The method of claim 18, wherein forming the plurality of hydrogenated silicon layers comprises: forming the plurality of hydrogenated silicon layers at a deposition rate between 0.8 nm / s and 1.2 nm / s.

Images