AR-concepts for hermetic wafer level packaging of uncooled FIR bolometer arrays

Uncooled FIR-bolometer image sensors are established in many applications like building inspections, cold bridge analyses and predictive maintenance. New fields of application are discovered, like automotive night vision, advanced presence detection, gesture recognition etc. but these require a lower cost, small form factor packaging of the μ-bolometer sensors. Wafer level packaging (WLP) is seen as the enabling housing technology compared to ceramic packages for high volume production. Monolithic integrated μ-bolometer image sensors require a vacuum packaging with vacuum level in the range of 10-3 mbar or less. The growing demand for reliability especially in automotive applications has also a large impact on the package construction. The overall challenge for high sensitive μ-bolometer sensors is to create a small package that allows for a maximum IR transmission at minimum cost. The work describes a wafer level technology on 200mm wafers with a hermetic sealing for large evacuated cavity dimensions with the process integration of different anti-reflective surface treatments. Cavities are created with 90μm thick poly-silicon frames in an additive deposition technology. The IR window region in the caps features different customer specific anti-reflective concepts. One approach is a double side moth eye pattern that can be designed to suppress short wavelength by destructive interference. It is possible to use different geometries of moth eyes in- and outside of the cavities to create a low cost filter. To reduce sunlight transmission a combination of moth eyes inside the cavities and a multi-layer filter coating outside can be achieved. The moth eyes patterns are realized in silicon wafers by reactive ion etching. To generate a high vacuum up to 10-4 mbar a getter with large exposed surface is required. A 3D structured getter solution is presented that generates a maximum getter surface in a small area in the c- p. First wafers with a good optical resolution and thermoelectric sensitivity have been achieved by a eutectic wafer bonding process

Hermetic packaging concept for laser diodes on wafer level

While discrete laser diodes may be evacuated and sealed on single die level using small metal TO packages like TO housings, it is obvious that high volume production for mobile applications requires a much more economical and small factor solution for the realization of transparent optical packages. We present here a solution that realizes glass packages with vertical emission window for laser diodes on 8" silicon substrates. The new process uses a high temperature glass forming process with a combination of two different glasses each having different melting points

Modular packaging concept for MEMS and MOEMS

Wherever technical systems detect objects in their environment or interact with people, optical devices may play an important role. Light can be relatively easily produced and spatially and temporally modulated. Laser can project sharp images over long distances or cut materials in short distances. Depending on the wavelength an invisible scanning in near infrared for gesture recognition is possible as well as a projection of brilliant colour images. For several years, the Fraunhofer ISIT develops Opto-Packaging processes based on the viscous reshaping of glass wafers: First, hermetically sealed laser micro-mirror scanners WLP with inclined windows deflect in the central light reflex of the window out of the image area. Second, housing with lateral light exit permits hermetic sealing of edge-emitting lasers for highest reliability and durability. Such systems are currently experiencing an extremely high interest of the industry in all segments, from consumer to automotive through to materials processing. Our modular Opto-Packaging platform enables fast product developments. Housing for opto mechanical MEMS devices are equipped with inclined windows to minimize distortion, stray light and reflection losses. The hot viscous glass forming technology is also applied to functionalized substrate wafers which possess areas with high heat dissipation in addition to thermally insulating areas. Electrical contacts may be realized with metal filled vias or TGV (Through Glass Vias). The modular system reduces the development times for new, miniaturized optical systems so that manufacturers can focus on the essentials in their development, namely their product functionalities

Silicon lens arrays for wafer level packaging of IR-sensors

A new process technology has been developed for a cost efficient production of refractive convex lenses made of silicon. These lenses are produced as lens arrays on standard eight inch Si-wafers to allow the optical capping of IR sensors in a wafer level packaging (WLP) process. A manufacturing process is described using a glass forming process with thin (50um) AF32® glass wafers. Si-spheres of well-defined diameter are transferred to a thin glass membrane on top of a Si-wafer with prefabricated cylindrical openings. In a thermal bonding process, the lens part of the Si-spheres sinks into the cavities while the outer part is grinded away. The resulting plano-convex lens calottes remain firmly embedded in the wafer surface. In this manner an array of Si-lenses on a Si-wafer is realized to be used as cover wafer for wafer level packaging of IR-sensor devices. First designs of Si-lens arrays have been fabricated. Starting with Si-spheres of radius of curvature 0.8 mm conv ex lenses of 0.82 mm diameter (aperture) and a sagittal height of 0.12 mm were produced

Precision micro-optical elements for manufacturing of gas sensors using IR-absorption

A growing number of micro optical electro-mechanical systems (MOEMS) are used in system applications like IR-detectors, projection displays or LIDAR systems. A new process technology has been developed for manufacturing precise optical components from borosilicate glass by 8-inch wafer batch processing. An improved process technology was applied for the first time for manufacturing of precise spherical mirrors of up to 8 mm diameter. The mirrors are assembled to realize a multiple reflection cell with low outer volume and a large internal optical absorption path. These cells are assembled as IR-absorption gas sensors. Quantities of precise lenses and mirrors can be produced at low costs by batch processing. The mirrors are covered with a metallic reflective coating. After that processing the optical elements are separated and mounted to realize a multi-reflection cell using two spherical mirrors. Examples for micromechanically actuated optical components are shown. With piezoelectric driven components a Fourier-Transformation IR-spectrometer might be set-up to be used in combination with the minimized absorption cell

New designs for MEMS-micromirrors and micromirror packaging with electrostatic and piezoelectric drive

Developments for miniaturized, MEMS based micromirrors are an active area of ongoing research due to the promising perspectives for cost efficient and precise picoprojectors and scanners for e.g. LID AR applications. In this article we report several devices of 1 -dim and 2-dim micromirrors based on new designs and new process capabilities using piezoelectric actuators. For micro-mirrors an 8Ⳡwafer-level packaging process was developed using preprocessed borosilicate glass wafers. An optimized design of an optical package is presented that avoids any stray reflexes and ghost images in laser projection applications. For 1 dim piezoelectric micro-mirrors, diameter 1.2 mm and 1 mm, scan angles in resonance mode of 40° and 73.2° at frequencies of 60 kHz and 27 kHz in ambient air have been achieved in various designs with driving voltages between 10 V and 15 V. Devices for 2-dim microscanners with electro-static and piezo-electric actuation are presented

Resonant biaxial 7-mm MEMSm mirror for omnidirectional scanning

Low-cost automotive laser scanners for environment perception are needed to enable the integration of advanced driver assistant systems (ADAS) into all automotive vehicle segments, a key to reducing the number of traffic accidents on roads. An omnidirectional 360 degree laser scanning concept has been developed based on combination of an omnidirectional lens and a biaxial large aperture MEMS mirror. This omnidirectional scanning concept is the core of a small sized low-cost time-of-flight based range sensor development. This paper describes concept, design, fabrication and first measurement results of a resonant biaxial 7mm gimbal-less MEMS mirror that is electrostatically actuated by stacked vertical comb drives. Identical frequencies of the two resonant axes are necessary to enable the required circle scanning capability. A tripod suspension was chosen since it allows minimizing the frequency splitting of the two resonant axes. Low mirror curvature is achieved by a th ickness of the mirror of more than 500 µm. Hermetic wafer level vacuum packaging of such large mirrors based on multiple wafer bonding has been developed to enable to achieve a large mechanical tilt angle of +/- 6.5 degrees in each axis. The 7mm-MEMS mirror demonstrates large angle circular scanning at 1.5kHz

Resonant biaxial 7-mm MEMS mirror for omnidirectional scanning

Low-cost automotive laser scanners for environmental perception are needed to enable the integration of advanced driver assistant systems into all automotive vehicle segments, which is a key to reduce the number of traffic accidents on roads. Within the scope of the European-funded project MiniFaros, partners from five different countries have been cooperating in developing a small-sized low-cost time-of-flight-based range sensor. An omnidirectional 360-deg laser scanning concept has been developed based on the combination of an omnidirectional lens and a biaxial large aperture MEMS mirror. The concept, design, fabrication, and first measurement results of a resonant biaxial 7-mm gimbal-less MEMS mirror that is electrostatically actuated by stacked vertical comb drives is described. Identical resonant frequencies of the two orthogonal axes are necessary to enable the required circle scanning capability. A tripod suspension was chosen, since it minimizes the frequency splitting of the two resonant axes. Low-mirror curvature is achieved by a thickness of the mirror of more than 500 pm. Hermetic wafer-level vacuum packaging of such large mirrors based on multiple wafer bonding has been developed to enable a large mechanical tilt angle of +/- 6.5 deg in each axis. Due to the large targeted tilt angle of +/- 15 deg and because of the MEMS mirror actuator having a diameter of 10 mm, a cavity depth of about 1.6 mm has been realized