Fabrication of MEMS zoom lens structure

A method for fabricating a MEMS zoom lens device. The device is formed substantially on a silicon substrate and includes control circuitry formed on the substrate, multiple actuators having charge areas for creating electrostatic fields, a flexible support for flexibly coupling a lens to the substrate, an electrostatic layer coupled to the lens. The charge areas act in response to the control circuitry to apply an electrostatic force to the electrostatic layer to move the lens with respect to the substrate and optical sensors or detectors. In a preferred embodiment, the flexible support is formed in a serpentine shape from silicon nitride. A stop support is formed to underlie the flexible support to prevent damage to the flexible support in a rest (i.e., non-zoomed) position.

BACKGROUND

Microelectromechanical (MEM) systems (MEMS), such as arrays of small mirrors controlled by electric charges, are known in the art. MEMS devices are desirable because of their small size, potential lower cost, and higher performance. Some types of devices that have been built using MEMS techniques include accelerometers, gyroscopes, temperature sensors, chemical sensors, AFM (atomic force microscope) probes, micro-lenses, actuators, etc. Such devices can be integrated with microelectronics, packaging, optics, and other devices or components to realize complete MEMS systems. Some examples of MEMS systems include inertial measurement units, optical processors, sensor suites, and micro robots.

Although MEMS techniques, and other related fields such as nanotechnology, have been used successfully to fabricate many types of devices, there are still various problems to be overcome in manufacturing increasingly complex devices.

SUMMARY

One embodiment of the invention provides a method for fabricating a MEMS zoom lens device. The device is formed substantially on a silicon substrate and includes control circuitry formed on the substrate, multiple actuators having charge areas for creating electrostatic fields, a flexible support for flexibly coupling a lens to the substrate, an electrostatic layer coupled to the lens. The charge areas act in response to the control circuitry to apply an electrostatic force to the electrostatic layer to move the lens with respect to the substrate and optical sensors or detectors.

In a preferred embodiment, the flexible support is formed in a serpentine shape from silicon nitride. A stop support is formed to underlie the flexible support to prevent damage to the flexible support in a rest (i.e., non-zoomed) position.

One embodiment of the invention provides a method for producing a microelectromechanical device, the method comprising: forming a substrate; forming a flexible support coupled to the substrate; coupling a lens to the flexible support so that the lens is flexibly coupled to the substrate; and forming one or more actuators for moving the lens with respect to an optical sensor.

DETAILED DESCRIPTION

FIG. 1shows a top view of a MEMS zoom lens assembly. Although embodiments of the invention are discussed with respect to specific structures, measurements, materials, arrangements or other characteristics, other embodiments can vary from those shown.

InFIG. 1, assembly100includes base110that can be a silicon substrate or other microelectronic or MEMS construct. Lens support post112attaches lens102to flexible support104. In a preferred embodiment four flexible supports are attached between the support post and base. Each flexible support is a formed in a serpentine shape to achieve spring-like properties so that the lens attached to the support post can be moved with respect to the base. An arrangement of “bumps” is used to prevent the flexible support structures from moving beyond a desired point. The bumps are shown inFIG. 1at, for example,103,105and107.

Four actuators106are provided at each corner of the assembly. Note that other embodiments can use more or less actuators. The actuators can be of different shapes (e.g., curved ring portions, elongated bars, etc.) and can be positioned at arbitrary locations on the base.

FIG. 2shows a side view of the assembly ofFIG. 1. In general, the same reference number used in different Figures denotes the same component. InFIG. 2, lens102is shown upon lens support post112which is attached to flexible support120. Lens102is provided with an electrostatic layer122along the bottom side of the lens. In other embodiments more than one lens may be used. Also, lenses can have different shapes and can be provided with one or more electrostatic layers in any suitable shape, size and fixed mounting relative to the lens(es). In some embodiments the electrostatic layer can be integral with, or a part of, the lens, as where part of the lens material, itself, is provided with a charge. Base110is shown on either side of flexible support120.

FIG. 3shows actuators130upon base110. Each actuator can selectively apply a force to electrostatic layer122as, for example, by using an electrostatic or magnetic effect. In a preferred embodiment, actuators exert a force upon the electrostatic layer in a region such as charge region132in actuator130. Charge regions in different actuators around the electrostatic layer are coordinated to cause the lens to raise or lower with respect to base110. Optical detectors beneath the lens (e.g., coupled to the base) detect light that passes through the lens in a direction AA–AB. Various of the structures—lens102, electrostatic layer122, support post112, flexible support120—can be made optically transparent, as desired. Details of the operation, structure and formation of an exemplary lens can be found in the related co-pending application, referenced above.

Next,FIGS. 4–18are discussed to provide details of a method of fabrication of a MEMS zoom lens assembly.

FIG. 4illustrates silicon substrate200that includes microelectronic circuit fabrication areas such as microelectronic circuit area210. Such circuitry can include any type of electrical component such as transistors, diodes, capacitors, conductors, resistors, etc. Any suitable process technology can be used to achieve, for example, metal oxide semiconductor (MOS), complimentary MOS (CMOS), bipolar, etc., components. The substrate can be made of any suitable material such as silicon, germanium, etc. In general, constructs described herein may be formed with any suitable materials and with any effective methods.

Photoresist layers204and206are applied to the top and back, respectively, of the substrate. A portion of back photoresist layer206is removed to expose the substrate. Actuator mounting block202is formed above the circuit area210. Note that inFIG. 4both the left and right sides of the assembly are symmetrical. That is, a back photoresist layer, circuit area and actuator mounting block are also formed on the right side of the substrate. The actuator mounting blocks allow control circuitry in the circuitry areas to control the actuators, as described below. A top layer of SiN is provided onto the substrate. Note that the order of formation of different components or constructs may vary in different fabrication approaches. It is anticipated that, for example, achieving the structure shown inFIG. 4will include several microelectronic and/or MEMS fabrication steps such as LOCOS process, well process, field formation, gate formation, chemical vapor deposition, metallization, reflow, etc.

FIG. 5shows a later stage in the fabrication of the assembly. InFIG. 5, substrate200has been boron doped in the area at the back of the substrate not covered by resist. SiN layer220is deposited on top of the top resist layer.FIG. 6, shows the result of a resist layer applied selectively (shown in solid black) and then etching the top SiN layer to provide bumps.FIG. 7shows the photoresist removed to reveal the SiN bumps.

FIG. 8shows a sacrificial layer of photoresist (solid black) applied over the bumps.FIG. 9shows a SiN deposition step. The SiN layer inFIG. 9is used to form the serpentine “springs” in a later step. Note that other designs can be used to achieve a flexible support for the lens. For example, other embodiments can use a more angular zig-zag pattern, less angular sinusoidal pattern, solid sheet of flexible material, etc. In some cases, three dimensional strands such as coiled springs might be used. In general, the flexible support can be any suitable shape or shapes. More than one type of material can be used. The SiN bumps are used to support the springs and prevent the springs, lens support and lens from going beyond a desired rest, or stop, position. This can be important, for example, to provide a calibrated non-zoom position, to protect the flexible support structure, and also to protect any optical sensors that may be positioned close to the lens.FIG. 10shows a stage where the serpentine springs have been formed by etching through the top resist mask (in solid black).FIG. 11shows the resist removed to leave the springs exposed. The larger structure at250is the central portion where the springs meet and where the support post will be formed.

FIG. 12shows a resist layer (solid black) patterned to allow formation of the lens support post from a SiN layer.FIG. 13shows the result of a blanket SiN etching step where only the support post formation at the middle of the springs remains.FIG. 14shows a Niobium Oxide electrostatic layer260formed by sputtering over the arrangement ofFIG. 13. Photoresist and etching steps are used to create gaps270,272around the perimeter of the electrostatic layer. Other materials used to fabricate semiconductor and/or microelectromechanical (MEM) machines may be used for these and the other structures shown and described, and fabrication may be done using known semiconductor and MEM machine fabrication procedures.

FIG. 15shows the fabrication at a stage after resist coating280has been applied to the top of the device. KOH back etching has been performed at the back of the device to remove the substrate in the area of282.FIG. 16shows the device after sacrificial ashing is used to remove the resist.

FIG. 17shows actuators302and304attached to the device with printed circuit board techniques. Electrodes, or charge generators, are set at accurate spacing with bump balls310and312. In other embodiments, different numbers, types and arrangements of electrodes are possible. Other techniques can be used to attach or fashion the actuators. Lens102is affixed to electrostatic layer by122using a mount process. In other embodiments different mounting processes may be used. For example, a wafer mount process might be used.

FIG. 18shows an alternative construction for the electrodes. InFIG. 18, the actuators and electrodes are made by a glass wafer process using a glass substrate, metallization and metal etching steps. Other fabrication methods may be used for the actuators and electrodes.

Although the invention has been described with respect to specific embodiments thereof, these embodiments are merely illustrative, and not restrictive, of the invention. Spaces shown within or around components or structures of the device may be filled with air, other gas or liquid, or there may be a substantial vacuum within the spaces. In some embodiments the lens apparatus can be sealed from the ambient environment, and in other embodiments the lens apparatus can be open to the ambient environment. The charges on the actuators may be variable by discrete or continuous amounts, controlled by either digital or analog control signals. In some embodiments, the charge position is moved on the one or more actuators, such as by charging two or more address electrodes in an addressable circuit. Control circuitry for the actuators may be formed in or on a portion of the base, or may be separate from the base.

Aspects of the invention may be realized on different size scales than those presented herein. Although MEMS techniques have primarily been presented, macro, nano or other designs, sizes and fabrication techniques may be used to advantage in different embodiments.

In the drawings, well known elements may be omitted so as to more clearly illustrate embodiments of the invention. For example, components and fabrication steps for semiconductor, microelectromechanical systems (MEMS), discrete components, etc., may be omitted and still achieve desired structures or results. Similarly, steps can be added without departing from the scope of the invention.

Further, as used herein, “above,” “below,” “underlying,” “overlying” and the like are used primarily to describe possible relations between elements, but should not be considered otherwise limiting. Such terms do not, for example, necessarily imply contact with or between elements or layers.

Embodiments of the invention may be implemented by using a programmed general purpose digital computer, by using application specific integrated circuits (ASICs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), optical, chemical, biological, quantum or nanoengineered systems, components and mechanisms may be used. In general, the functions of the present invention can be achieved by any means as is known in the art. Distributed, networked systems, and/or components and circuits can be used. Communication, or transfer, of data may be wired, wireless, or by any other means.