Patent Application
20180307039
The present invention relates generally to a Micro-Electromechanical System (MEMS)-based optical modulators with distributed mirrors for high power handling and to methods of manufacturing and using the same.
Laser processing systems are widely used and growing in popularity for a number of different applications including cutting, marking, engraving, printing, testing and measuring. For example, laser engraving and imaging systems are used to form designs, such as text, logos, or other ornamental designs, on and/or in workpieces. Current state-of-art laser processing systems use a high power laser and a galvo-scan mirror to scan a single beam over a metal, plastic, wood or paper workpiece to form a design. Because of this the time required to form a design on a single workpiece using a conventional laser processing system is unacceptably long. Moreover, because in many conventional systems the workpiece is moved relative to the single laser beam the resolution and complexity of the design can be adversely affected.
MEMS-based spatial light modulators offer the prospect of greatly improved throughput over single-beam laser write systems. While it is desirable to use MEMS-based spatial light modulators in conjunction with high-power continuous wave (CW), nano-, pico-, and femto-second lasers, a variety of damage mechanisms preclude reliable operation with high-fluence applications. For CW and nano-second lasers, thermal degradation modes dominate. For example, in the “Soret effect”, atoms of a reflector material physically migrate from hotter regions to cooler regions, reducing the reflection efficiency of the SLM and accelerating further damage. For pico- and femto-second lasers, ablative damage modes dominate. Here, the peak pulse energies vaporize or otherwise degrade the reflector material. Both the thermal and ablative damage mechanism hinge on the reflectivity of the light-reflecting layer of the MEMS-based SLM. If the reflectivity is high enough, only minimal laser energy is transmitted to the mirror and MEMS structure. Accordingly, there is a need for enhanced reflectivity MEMS light modulators to enable the next generations of high-power laser processing systems.
In a first aspect, a method for fabricating a MEMS-based high power handling optical spatial light modulator (SLM) modulator is provided. The method includes or involves forming a number of electrostatically deflectable elements over a surface of a substrate, each electrostatically deflectable element including a mechanical layer and an electrode layer, followed by forming a non-metallic, multilayer optical reflector over each electrostatically deflectable element. The multilayer optical reflector includes at least a first layer of high index material having a high index of refraction, a second layer of a low index material having a low index of refraction formed over the first layer, and a third layer of high index material having a high index of refraction formed over the second layer. At a minimum, the high index and low index materials are selected and deposited to ensure that the overall stress stays tensile. Generally, the high index materials and low index material are selected and deposited to maintain planarity of the multilayer optical reflector at operating temperature. In one embodiment, the high index materials include silicon-germanium, and the low index material is air or an air-gap formed between the first and third layers of the high index materials.
In a second aspect a MEMS-based high power handling optical spatial light modulator (SLM) modulator is provided including a number of electrostatically deflectable elements suspended over a surface of a substrate, and a non-metallic, multilayer optical reflector over each electrostatically deflectable element. Each electrostatically deflectable element includes a mechanical layer and an electrode layer. The multilayer optical reflector includes at least a first layer including a first high index material having a high index of refraction, a second layer including a low index material having a low index of refraction formed over the first layer, and a third layer including a second high index material having a high index of refraction formed over the second layer. In some embodiments, the mechanical layer includes a tensile silicon-germanium, and the first and second high index materials and the low index material are selected and deposited to maintain planarity of the multilayer optical reflector at operating temperature. Suitable materials for the first and second high index materials can include monocrystalline silicon (Si), poly-crystalline silicon, amorphous silicon, silicon-nitride (SiN), silicon-germanium (SiGe), silicon-carbide, titanium-oxide (TiO2) or zirconium-oxide (ZrO2). Suitable low index materials having a low index of refraction (n) include silicon-dioxide (SiO2), silicon-nitride, germanium, air or a MEMS fill gas, such as a mixture of one or more of nitrogen, hydrogen, helium, argon, krypton or xenon gases.
Embodiments of the present invention will be understood more fully from the detailed description that follows and from the accompanying drawings and the appended claims provided below, where:
Embodiments of laser processing systems including a Micro-Electromechanical System (MEMS) devices based optical switch or optical modulator with distributed mirrors for high power handling and to methods of manufacturing and using the same are described herein with reference to figures. However, particular embodiments may be practiced without one or more of these specific details, or in combination with other known methods, materials, and apparatuses. In the following description, numerous specific details are set forth, such as specific materials, dimensions and processes parameters etc. to provide a thorough understanding of the present invention. In other instances, well-known semiconductor design and fabrication techniques have not been described in particular detail to avoid unnecessarily obscuring the present invention. Reference throughout this specification to “an embodiment” means that a particular feature, structure, material, or characteristic described in connection with the embodiment is included in at least one embodiment of the invention. Thus, the appearances of the phrase “in an embodiment” in various places throughout this specification are not necessarily referring to the same embodiment of the invention. Furthermore, the particular features, structures, materials, or characteristics may be combined in any suitable manner in one or more embodiments.
The terms “over,” “under,” “between,” and “on” as used herein refer to a relative position of one layer with respect to other layers. As such, for example, one layer deposited or disposed over or under another layer may be directly in contact with the other layer or may have one or more intervening layers. Moreover, one layer deposited or disposed between layers may be directly in contact with the layers or may have one or more intervening layers. In contrast, a first layer “on” a second layer is in contact with that second layer. Additionally, the relative position of one layer with respect to other layers is provided assuming operations deposit, modify and remove films relative to a starting substrate without consideration of the absolute orientation of the substrate.
The optical modulator can be either a binary optical switch in which the reflectance is switched between high and low states, or an analog optical modulator with gray scale capability in which either the phase or intensity of light reflected from the optical modulator can be continuously modulated.
Furthermore, the optical modulator can include either a single, individual pixel or multiple pixels ganged together in a one-dimensional (1D) or two-dimensional (2D) array to create a high power spatial light modulator (SLM). Suitable optical modulators include a ribbon-type optical modulator, such as a Grating Light Valve (GLV™), or a Planar Light Valve (PLV™), from Silicon Light Machines, Inc., of Sunnyvale, Calif.
A ribbon-type optical modulator, such as a GLV™, including a number of distributed mirrors or reflectors formed thereon to modulate a beam of light generated by a laser will now be described with reference to
Referring to
A schematic sectional side view of a movable structure or ribbon 102a of the optical modulator 100 of
Generally, the mechanical layer 116 comprises a taut silicon-nitride (SiN) or silicon-germanium (SiGe) film or layer, and flexibly supported above the surface 106 of the substrate 108 by a number of posts or structures, typically also made of silicon-nitride or silicon-germanium, at both ends of the ribbon 102a. The conducting layer 112 can be formed over and in direct physical contact with the mechanical layer 116, as shown, or underneath the mechanical layer. The conducting layer 112 or ribbon electrode can include any suitable conducting or semiconducting material compatible with standard MEMS fabrication technologies. For example, the conducting layer 112 can include an amorphous or polycrystalline silicon-layer, or a titanium-nitride (TiN) layer. Alternatively, if the reflective layer 118 is above the conductive layer 112, the conductive layer could also be metallic.
The separate, discrete reflecting layer 118, where included, can include any suitable metallic, dielectric or semiconducting material compatible with standard MEMS fabrication technologies, and capable of being patterned using standard lithographic techniques to form the reflective surface 104.
Another type of MEMS-based optical modulator for which the distributed mirror of the present invention is particularly useful is a Planar Light Valve or PLV™ from Silicon Light Machines, Inc., of Sunnyvale, Calif. Referring to
Individual actuators 206 or groups of actuators are moved up or down over a very small distance (typically only a fraction of the wavelength of light incident on the light valve 200) relative to first planar distributed mirror 203 of the face-plate 202 by electrostatic forces controlled by drive electrodes 214 in the substrate 210 underlying the actuators 206. Preferably, the actuators 206 can be displaced by n*λ/4 wavelength, where λ is a particular wavelength of light incident on the first and second planar distributed mirrors 203, 207, and n is an integer equal to or greater than 0. Moving the actuators 206 brings reflected light from the second planar distributed mirror 207 into constructive or destructive interference with light reflected by the first planar distributed mirror 203 (i.e., the face-plate 202), thereby modulating light incident on the light valve 200.
For example, in one embodiment of the light valve 200 shown in
In an alternative embodiment, not shown, the distance (D) between reflective layers of the face-plate 202 and actuator 206 can be chosen such that, in the actuator's quiescent state, the first and second distributed mirrors 203, 207 are displaced from one another by an even multiple of λ/4, such that the light valve 200 in quiescent state is reflecting, and in an active state, as illustrated by the right actuator, the actuator is displaced by an odd multiple of λ/4 causing it to scatter incident light.
A close up planar view of a single actuator is shown in
A schematic block diagram of a sectional side view of the actuator 206 of
Although the light reflective surface of the actuator 206 is shown and described above as being positioned below the light reflective surface 203 of the face-plate 202 and between the first reflective surface and the upper surface of the substrate, it will be appreciated that the distributed mirror 207 of the actuator can alternatively be raised above the movable actuator so as to be positioned coplanar with or above the light reflective surface of the face-plate 202.
In an alternative embodiment of a PLV™, an individual modulator 300 of which is shown in
In one embodiment, shown in
In an alternative embodiment, shown in
A graph illustrating the reflection 500, transmission 502 and absorption 504 of a distributed or Bragg mirror including alternating transmissive layers of poly-crystalline silicon, silicon-dioxide and poly-crystalline silicon at near-infrared (NIR) wavelengths of from about 700 to 1000 nanometers (nm) is shown in
In other embodiments, the distributed mirror can include a stack of transmissive layers overlying an absorbing layer on the mechanical layer of a MEMS-based optical modulator to absorb and re-emit, or reflect light incident thereon. The absorbing containing layer can include any suitable metal aluminum (Al), silver (Ag), gold (Au), chrome (Cr), copper (Cu), nickel (Ni), platinum (Pt), palladium (Pd), titanium (Ti), tungsten (W) or mixtures or alloys thereof. Referring to
In an alternative embodiment, shown in
Suitable materials for the stack of transmissive layers 1802 can include dielectrics or doped semiconductors including poly-crystalline silicon, silicon-dioxide, titanium-oxide, silicon-carbide, aluminum-arsenide, zirconium-oxide and titanium-oxide. Suitable materials for the absorbing layer 1804 can include substantially pure aluminum or thermally compatible aluminum containing alloys.
A graph illustrating the reflection 1900, transmission 1902 and absorption 1904 of a Bragg mirror including a stack of transmissive layers overlying an aluminum absorbing layer, and including alternating first and third reflective layers of silicon-carbide and second and fourth reflective silicon-dioxide at wavelengths of from about 350 to about 1500 nm is shown in
Optionally, the aluminum absorbing layer 1804 can further serves to prevent residual light from being transmitted to underlying regions, and/or as the electrode in a deflectable ribbon or actuator layer, as shown and described in connection with
In addition, it will be understood that the aluminum layer 1804 can be included within Bragg mirror 402 shown and described above in
In another aspect, the present disclosure is directed to a material processing system or laser processing system including a number of MEMS-based optical modulators, each including a number of distributed mirrors or reflectors, grouped or ganged together in a one dimensional (1D) or two-dimensional (2D) array to create a high power spatial light modulator (SLM). Material or laser processing systems, also known as laser-based material processing systems are particularly useful in additive manufacturing processes, such as selective laser sintering (SLS), selective laser melting, sintering, oxidation, reaction, ablation or other laser-induced material modification. By selective laser melting it is meant an additive manufacturing process that uses high energy, typically in the form of a laser beam, to create three-dimensional parts by fusing fine a powder of a material, such as metal, together on a surface of substrate or workpiece. By selective laser sintering it is meant an additive manufacturing process that uses a laser as the power source to sinter powdered material (typically metal), binding the material together to create a solid structure. It is similar to selective laser melting, but differs in that the material is not fully melted allowing different properties, such as crystal structure, porosity, etcetera.
An embodiment of a laser processing system suitable for use in additive manufacturing processes will now be described with reference to
Generally, the illumination optics include a number of elements including lenses, mirrors and prisms, designed to transfer a light beam from the laser 2004, such as an Ultra Violet laser, to the MEMS-based SLM 2002 to illuminate an area substantially equal to that of the reflective surface of the MEMS-based SLM. In the embodiment shown, the illumination optics include a polarizing beam splitter (PBS) 2022, which reflects light having a first polarization onto the MEMS-based SLM 2002, and transmits the light having a second polarization from the MEMS-based SLM towards a target wafer or workpiece 2024 through the imaging optics. For example, the PBS 2022 can be adapted to reflect light having a Transverse-Electric (TE) polarization towards the MEMS-based SLM 2002, and to transmit light having a Transverse-Magnetic (TM) polarization toward the target workpiece 2024. The light that is initially directed toward the MEMS-based SLM 2002 by the PBS 2022 in the TE state will pass twice through a quarter-wave plate (QWP) 2026, thus converting it to TM polarization and allowing to pass through the PBS and on to the imaging optics that follow.
As shown, the imaging optics can include magnification and filtering elements, such as a first Fourier Transform (FT) lens 2028 to focus and direct light from the PBS 2022 onto a FT filter 2030 to select the 0th order modulated light, and a second, larger Inverse FT lens 2032 to enlarge the image generated by the SLM 2002 and project it onto the target substrate 2024
Another embodiment of a laser processing system using phase modulation and including a MEMS-based SLM including a number of distributed mirrors or reflectors formed thereon to modulate a beam of light generated by a laser will now be described with reference to
In accordance with another embodiment of the invention of the present disclosure, and similar to the laser processing system 2000 of
Generally, the illumination optics include a number of elements including lenses, mirrors and prisms, designed to transfer a light beam from the laser 2104, such as an Ultra Violet laser, to the MEMS-based SLM 2102 to illuminate an area substantially equal to that of the reflective surface of the MEMS-based SLM. In the embodiment shown, the illumination optics include a PBS 2122, which reflects light having a first polarization onto the MEMS-based SLM 2102, and transmits the light having a second polarization from the MEMS-based SLM towards a target wafer or workpiece 2124 through the imaging optics. For example, the PBS 2122 can be adapted to reflect light having a TE polarization towards the MEMS-based SLM 2102, and to transmit light having a TM polarization toward the target workpiece 2124. The light that is initially directed toward the MEMS-based SLM 2102 by the PBS 2122 in the TE state will pass twice through QWP 2126, thus converting it to TM polarization and allowing to pass through the PBS and on to the imaging optics that follow.
As shown, the imaging optics can include magnification and filtering elements, such as a FT lens 2128 to focus and direct light from the MEMS-based SLM 2102 onto a FT filter, a FT filter 2130 to select the 0th order modulated light, and a second, larger Inverse FT lens 2132 to enlarge the image generated by MEMS-based SLM and project it onto the target workpiece 2124.
A method for processing a workpiece using the laser processing system of
In yet another aspect, the present disclosure is directed to a MEMS-based optical spatial light modulator having a non-metallic, multilayer optical reflector, capable of handling high-power lasers such as those used in the applications described above.
Metallic coatings, such as aluminum, are commonly used as reflectors in conventional mems spatial light modulators because these coatings exhibit good reflectivity across a wide spectral band, and because tools for forming such metallic coatings are widely available in semiconductor and MEMS foundries. However, metal coatings typically have low melt temperatures and relatively high chemical activity limiting the lifetime of modulators with metallic reflectors in applications using high fluence or high power lasers. Aluminum in particular has a relatively low melt temperature of about 660° C. Additionally, it has been observed metals migrate under high thermal gradients due to the Soret effect, and can oxidize or undergo other chemical reactions under UV illumination, reducing the reflectivity of the reflectors. The above problems and eliminated by the use of non-metallic, multilayer optical reflectors.
The high power handling optical modulators with distributed mirrors according to an embodiment of the present disclosure are also particularly useful in additive three dimensional (3D) printing systems. 3D printing systems can use either a photopolymerization technology or Selective laser sintering (SLS). In photopolymerization is a liquid photopolymer or resin is exposed to a modulated beam of light that converts the liquid into a solid, building an object to be printed from a series of two-dimensional layers. Selective laser sintering involves melting and fusing together of fine, typically metal, particles using a high power laser to build successive cross-sections of an object.
An embodiment of a polymerization 3D printing system will now be described with reference to
As shown, the imaging optics can include magnification and filtering elements, such as a first Fourier Transform (FT) lens 2320 to focus and direct light from the PBS 2318 onto a FT filter 2322 to select the 0th order modulated light, and a second, larger Inverse FT lens 2324 to enlarge the image generated by the SLM 2302 and project it onto a surface of the resin 2308 immediately above or adjacent to the work surface 2312.
The transport mechanism 2310 is adapted and controlled by the controller 2316 to lower the work surface 2312 into the vat 2306 as the modulated light converts the resin 2308 into a solid, building successive layers or cross-sections of the object 2314 to be printed. Generally, the layers can be from about 100 μm to 1 mm thick. Optionally, the transport mechanism 2310 can be further adapted to move or reposition the work surface 2312 laterally to enable simultaneous printing of multiple objects or objects larger than the area imaged onto the work surface.
In one embodiment, the MEMs-based optical spatial light modulator is a ribbon-type is a ribbon-type spatial light modulator, such as that shown above and described with reference to
In another embodiment, the MEMs-based optical spatial light modulator is a Planar Light Valve or PLV™, such as that shown above and described with reference to
In an alternative embodiment of the PLV™, shown in
The face-plate 2402 is supported by one or more posts 2412 at corners of the modulator 2400, and can be formed solely by layers of the first optical reflector 2404. Alternatively the face-plate 2402 can further include a uniform, planar sheet of a dielectric or semiconducting material, for example a taut silicon-nitride or silicon-germanium layer, over which the first optical reflector 2404 is formed.
The movable actuator 2410 further includes in addition to the second optical reflector 2408 a mechanical layer 2414 and an actuator electrode or electrode layer 2416 separated from the second optical reflector 2408 by a central support 2418. The mechanical layer 2414 can include a taut layer of a material, such as silicon-nitride or silicon-germanium, supported by posts 2412 at corners of the modulator 2400. The electrode layer 2416 can include a metal or other conductive material, such as a doped poly-crystalline silicon, formed on the mechanical layer 2414, and is electrically coupled to ground or to drive electronics (not shown in this figure) through electrically conductive vias 2420 formed in or over one or more of the posts 2412. In operation, the movable actuator 2410 is deflected towards a lower electrode 2422 formed in or on the substrate 2424 by electrostatic forces generated when a voltage is applied between the base electrode and the electrode layer 2416 in the movable actuator.
It is noted that although the electrode layer 2416 is shown as being formed on top of the mechanical layer 2414, this need not be the case in every embodiment, and that the mechanical layer can alternatively be formed on top of the electrode layer. This later embodiment is particularly advantageous where the second optical reflector 2408 is separated from the mechanical layer 2414 and the electrode layer 2416 by the central support 2418, and the mechanical layer and the central support are formed from the same material.
In some embodiments, the non-metallic, multilayer optical reflectors include multiple interleaved or alternating layers of material having a high index of refraction and a material having a low index of refraction at a target wavelength of light to be modulated by the optical modulator. By a high index of refraction (n) it is meant a refraction of from about 2.6 to about 4.0 or more at target wavelengths of from 550 nm to 2 μm (2000 nm). By a low index of refraction (n) it is meant a refraction of from about 1.0 to about 2.0 at the target wavelengths. These alternations of layers having a high index of refraction with layers having a low index of refraction provide high reflectivity at interfaces of the layers. Additionally, both high and low index materials are further selected to have a low absorption (k) at the target wavelength. By a low absorption it is meant a material absorb less than one percent (1%) of light incident on the reflector. Suitable high index materials having a high index of refraction (n) include semiconductors and materials such as monocrystalline silicon (Si), poly-crystalline silicon, amorphous silicon, silicon-nitride, silicon-germanium, silicon-carbide, titanium-oxide (TiO2) or zirconium-oxide (ZrO2) Suitable low index materials having a low index of refraction (n) include silicon-dioxide, silicon-nitride, germanium, air or a MEMS fill gas. By a MEMS fill gas it is meant a gas or mixture of gases introduced during manufacture to fill spaces between layers and elements of the MEMS optical modulator, which is then hermetically sealed. The MEMS fill gas can be used to reduce corrosion of materials MEMS optical modulator, increase thermal transfer between layers and elements, and maintain or enhance optical characteristics of the MEMS optical modulator. Suitable fill gases can include pure form or mixtures of one or more of nitrogen, hydrogen, helium, argon, krypton or xenon gases.
Generally, the number of layers in the multilayer optical reflector is selected to be symmetrical about a mid-plane of the reflector, with equal numbers of layers above and below the mid-plane, and to be symmetrical about a neutral axis of the reflector to balance stresses and maintain optical planarity. Thus, the optical reflector can include from three to about twenty-one alternating layers of high and low index material. At a minimum, the high index and low index materials are selected and deposited to ensure that the overall stress stays tensile. Generally, the high index materials and low index material are selected and deposited such that the multilayer optical reflectors may be non-planar at a low, ambient temperature, such as at room temperature, due to differing thicknesses and coefficients of thermal expansion (CTE) of the layers, but become optically planar when raised to an operating temperature of the optical modulator, for example, by a high powered laser or light source.
Additionally, the thicknesses of the high and low index layers are selected or adjusted so as to substantially equal one quarter wavelength of the target wavelength of the light propagating in the material of the layer according to or based on the refractive index of the material.
It is further noted that the material and thickness of a particular layer may, but need not be the same as that of any other layer of high or low index material. By selecting the thicknesses and material of the high index and low index layers, and the number of pairs of layers in the multilayer reflector it is possible to achieve reflectivity of from about 90% to greater than 99%, while providing improved power handling as compared to conventional aluminum reflectors. It is further noted that the power handling is improved by reduced absorption relative to a conventional aluminum reflector, which typically has absorption of 4% or more, and by higher melting temperatures of the high and low index materials, which enables the non-metallic, multilayer reflector to be operated at longer periods at of higher laser fluence. For example, silicon-dioxide has a melting temperature of about 1710° C., while silicon has a melting temperature of about 1414° C. and Germanium has a melting temperature of about 982° C.—all substantially higher than the 660° C. melting temperature of aluminum used in conventional, metallic reflectors.
Where the electrostatically deflectable element is a ribbon of a ribbon-type modulator or an actuator of a stepped PLV™, such as shown and described with reference to
Alternatively, where the electrostatically deflectable element is an actuator of a PLV™ having a reflector physically separated from the mechanical layer by a center support, as shown and described with reference to
Optionally, by proper selection of the high index material and thickness of the first layer 2504 both the mechanical layer and the first layer of the first reflector 2404 on the face-plate 2402 and second reflector 2410 on the electrostatically deflectable element 2507 or actuator can be formed from a single, taut or tensile silicon-nitride or silicon-germanium layer, which serves or functions as both the mechanical layer 2506 and the first layer 2504 of the multilayer optical reflector 2502 for both the face-plate and the actuator.
In yet another embodiment, the mechanical layer 2506, the electrode layer 2516 and the first layer 2504 of the multilayer optical reflector 2502 can be formed from a single, taut or tensile silicon-germanium layer, which serves or functions as the mechanical layer, the electrode layer and the first layer of the multilayer optical reflector 2502 on the electrostatically deflectable element 2507 or actuator, and the mechanical layer and the first layer of the multilayer optical reflector on the face-plate 2402.
In one version of the above embodiments, the high index material of the first, third and fifth layers include silicon-germanium layers having an index of refraction (n) of about 4.0 at a target wavelength of 850 nm, and thicknesses of about 45 nm. The low index material of the second and fourth layers include silicon-dioxide layers having an index of refraction (n) of about 1.4 at the target wavelength, and a thicknesses of about 146 nm, to provide a reflectance of 99% or greater and an absorption of less than about 1%.
In other embodiments, the low index material is or includes air, and the non-metallic, multilayer optical reflector includes layers of high index material interleaved or separated by air-gaps.
The optical reflector can include from three to about twenty-one alternating layers of high index material and air-gaps, where the number of layers in the multilayer optical reflector is selected to be symmetrical about a mid-plane of the reflector, with equal numbers of layers above and below the mid-plane, and wherein the reflector is symmetrical about a neutral axis of the reflector to balance stresses and maintain optical planarity. Generally, as in the embodiment shown the reflector 2602 further includes a number of periodic mechanical connections or posts 2614 between layers of high index material in order to maintain the air-gaps 2606, 2610. The first and second air-gaps can be formed by deposition and subsequent removal of sacrificial layers between the layers of high index material, as explained in greater detail below. The posts 2614 can be composed of the same material as the first, third and fifth layers and are typically formed concurrently with an overlying layer, by patterning the sacrificial layer prior to depositing the high index material.
In one version of this embodiment, the high index material of the first, third and fifth layers include silicon-germanium layers having an index of refraction (n) of about 4.0 at a target wavelength of 850 nm, and thicknesses of about 45 nm, and the air-gaps of the second and fourth layers have an index of refraction (n) of about 1.0 at the target wavelength, and a thicknesses of about 200 nm, to provide a reflectance of 99% or greater and an absorption of less than about 1%.
In addition to the high power handling capabilities of the multilayer optical reflector 2502 of
Graphs illustrating the reflection 2700, transmission 2702 and absorption 2704 of a non-metallic, multilayer reflector at visible (VIS) to near-infrared (NIR) wavelengths of from about 600 to 900 nm are shown in
Methods of fabricating an optical modulator including a non-metallic, multilayer optical reflector on an electrostatically deflectable element according to an embodiment of the present disclosure will now be described. In a first embodiment, described with reference to the flowchart of
Referring to
Next, a mechanical layer of the actuator is formed over the first sacrificial layer by depositing a tensile layer over the first sacrificial layer, filing the holes to form the posts and the mechanical layer of the actuator (2804). The tensile mechanical layer can include silicon-nitride (SiN) or silicon-germanium. Generally, forming the mechanical layer further includes patterning mechanical layer to form flexures as shown in
A second sacrificial layer is then deposited over the patterned mechanical layer and electrode layer and patterned (2808). Again the sacrificial layer can include either poly-crystalline silicon or germanium. The thickness of the second sacrificial layer determines a separation between the actuator and face-plate of the optical modulator, thus the thickness will depend on whether the optical modulator is a PLV™ having a co-planar 1st and 2nd reflectors as shown in
Next, a first layer of high index material is deposited over the second sacrificial layer to fill the holes for the posts and the center support, and to form a first layer of the reflector over the face-plate and over the center support (2810). The high index material can include silicon, poly-crystalline silicon, silicon-germanium or titanium-oxide (TiOx2), and is deposited using CVD to a thicknesses selected to equal one quarter wavelength of the target wavelength in the high index material, adjusted according to their refractive index. For example, in one embodiment of the reflector shown in
In those embodiments in which the material of the low index layers in the reflector is air (air-gaps) as shown in
Next, a second layer of high index material is deposited over the third sacrificial layer to fill the holes for periodic mechanical connections or posts and to form a third layer of the reflector (2816). The high index material can include silicon, poly-crystalline silicon, silicon-germanium or titanium-oxide (TiOx2), and is deposited using CVD to a thicknesses selected to equal one quarter wavelength of the target wavelength in the high index material. For example, in one embodiment of the optical modulator shown in
A fourth sacrificial layer is then deposited over the second layer of high index material (the third layer of the reflector) and patterned (2818). Again the sacrificial layer can include silicon-germanium, and has a thickness equal to one quarter wavelength of the target wavelength in air. In embodiments in which the high index material of reflector is silicon-germanium the sacrificial layer is germanium. For example, in the embodiment of the reflector shown in
Next, a third layer of high index material is deposited over the third sacrificial layer to fill the holes for periodic mechanical connections or posts and to form a fifth layer of the reflector (2820). The high index material can include silicon, poly-crystalline silicon, silicon-germanium or titanium-oxide (TiOx2), and is deposited using CVD to a thicknesses selected to equal one quarter wavelength of the target wavelength in the high index material. For example, in one embodiment of the of the reflector shown in
Finally, a mask is formed over the third layer of high index material (the fifth of top layer of the reflector) and the layers of the reflector etched to form the first reflector on the face-plate and the second reflector over the actuators, to subsequently substantially remove all sacrificial layers releasing the actuators and forming first and second air-gaps of the reflectors between the first, second and third layers of high index material (2822). Generally, etch and release is accomplished in a single wet or dry etch step.
The method of
Similarly, it will be understood that the method can also be used to form a GLV™ or ribbon-type optical modulator in which the electrostatically deflectable elements are ribbons, and having non-metallic, multilayer reflectors including either solid dielectric layers or air-gaps. In one embodiment, the method for fabricating ribbon-type optical modulator is identical to that described above up to the deposition of the electrode layer, step 2806. Thereafter, the first semiconductor layer, the first layer of the reflector, is formed directly on the electrode layer, step 2812, and the method continues substantially as described above to form reflectors including air-gaps. Alternatively, reflectors having solid dielectric layers, as shown in
Thus, embodiments of MEMS-based optical modulators with non-metallic, multilayer reflectors and methods of fabricating and using the same have been described. Although the present disclosure has been described with reference to specific exemplary embodiments, it will be evident that various modifications and changes may be made to these embodiments without departing from the broader spirit and scope of the disclosure. Accordingly, the specification and drawings are to be regarded in an illustrative rather than a restrictive sense.
The Abstract of the Disclosure is provided to comply with 37 C.F.R. § 1.72(b), requiring an abstract that will allow the reader to quickly ascertain the nature of one or more embodiments of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims. In addition, in the foregoing Detailed Description, it can be seen that various features are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed embodiments require more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.
Reference in the description to one embodiment or an embodiment means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the circuit or method. The appearances of the phrase one embodiment in various places in the specification do not necessarily all refer to the same embodiment.
This application is a continuation-in-part of co-pending U.S. application Ser. No. 15/297,047, filed Oct. 18, 2016, which is a continuation-in-part of Ser. No. 14/673,276, filed Mar. 30, 2015, now abandoned, which claims the benefit of priority under 35 U.S.C. 119(e) to U.S. Provisional Patent Application Ser. No. 61/201,887, filed Sep. 22, 2014, all of which applications are hereby incorporated by reference in their entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61201887 | Dec 2008 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 15297047 | Oct 2016 | US |
| Child | 16010148 | US | |
| Parent | 14673276 | Mar 2015 | US |
| Child | 15297047 | US |
