Chih-Chun Lee

The implementation of concave micro optical devices using a polymer dispensing technique

This study demonstrates a novel approach to implementing a double-concave (DCV) microlens using a simple polymer dispensing and sucking process. The DCV microlens is implemented at room temperature using a commercially-available pneumatic-controlled polymer dispensing system. The DCV lens profile can be tuned by varying the volume of the dispensed polymer. It is also easy to integrate the present polymer DCV microlens with other suspended micromachined devices such as silicon nitride film and silicon-on-glass (SOG) micromachined structures. This study further employs the process for DCV to implement a concave mirror. The measurement results show a typical DCV lens (made of NOA63 polymer) with negative focal lengths of −1.42 mm (red laser) and −1.17 mm (blue laser), and a concave mirror with a focal length of 3.28 mm. Moreover, this study also demonstrates the integration of a DCV microlens with other optical components, such as plano-convex and double-convex lenses. (Some figures in this article are in colour only in the electronic version)

Implementation of a micro ball lens on a silicon optical bench using insoluble two-phase liquid immersion technology

This paper presents a two-phase liquid micro lens formation technology to implement a polymer micro ball lens. A UV-curable polymer is dispensed into a buffer liquid to form the ball lens. The buffer liquid provides a gravity-free condition so that the ball lens has a highly symmetric shape. The diameter of the ball lens is controlled by the volume of the dispensed polymer. This technology implements either a discrete optical component, or a ball lens integrated with a MEMS (micro electrical mechanical system) structure to form a SiOB (silicon optical bench). To demonstrate the feasibility of this study, ball lenses with diameters ranging from 200 to 600 µm and root mean square (RMS) surface roughness of about 10 nm are fabricated using a commercial UV-curable polymer. The average roundness of a 550 µm diameter ball lens observed from different angles is 3.3 ± 0.4 µm. The peak-to-valley and RMS wavefront errors of a 550 µm diameter ball lens measured by a Mach–Zehnder interferometer are 0.3744 waves (237 nm) and 0.0766 waves (48 nm), respectively. The measured back focal length is about 99 µm, and the associated effective focal length is about 351 µm. The integration of such polymer micro ball lenses with suspended micromachined Si3N4 structures to form the SiOB is also demonstrated.

Design and implementation of a novel “polymer joint” for thermal actuator current and thermal isolation

This study presents a novel thermal isolation component “polymer joint” to reduce the current and heat flow (by conduction) between micro thermal actuators. An optical stage consisted of V-beam thermal actuators for optical-tracking and thermal-driven focal-length tunable micro polymer lens for optical-focusing is employed to demonstrate the present concept. To overcome the thermal coupling of these two actuators by heat-conduction, the two components fabricated by SOI wafer (Si∼150W/m-k) are connected by the low thermal conductivity joints (polymer∼0.2W/m-k). The displacement provides by the V-beam actuator is about ±13µm. The temperature difference is about 80°C measurement by infrascope. The variation of micro lens radius of curvature is about 1%.

3D integration of micro optical components on flexible transparent substrate with through-hole- vias

This study establishes the polymer-stacking and metal-electroplating processes on Si-substrate to implement a flexible and transparent substrate with alignment mesa, distributed though-hole-vias, and multi-layer electrical routings. This process is especially useful for 3D integration of micro optical components on flexible substrate. The integrated chips can be further protected and sealed by an additional parylene coating. More micro-optical components can also be vertically integrated by additional polymer molding. To demonstrate the feasibility of this approach, LED chips are bonded and sealed in flexible substrate, and the polymer microlens is further integrated with the lighting chips using molding process. The lighting of packaged LED chips is demonstrated in both air and water.

Design and implementation of a miniature polymer ball bearing slide table

This study presents a novel design and fabrication process to realize a miniature polymer ball bearing slide table (slider) with long linear travel range. The linear slide table consists of a pair of V-shape silicon (111) crystal plane rails, and a suspended slider supported by four polymer ball bearings. The ball-housing on slider is also designed to confine the bearing. The slider, rails, and ball-housings are patterned by DRIE and wet anisotropic etching on double-polished (100) wafer. The ball bearings are fabricated and in-situ self-assembled using the liquid polymer formation technique in buffer liquid. After polymer solidified by UV-curing, the ball bearing is confined in ball-housing. The device is successfully implemented and the traveling test is also demonstrated using magnetic force.

Implementation of polymer-dispersed liquid crystal microprism array for LED radiation pattern application

This study implements a novel lighting chip with tunable radiation pattern. The lighting chip consists of polymer-dispersed liquid crystal (PDLC) microprism array, LED, and Si-carrier. By integrating the characteristics of microprism and the scattering/transmitting modes of PDLC, the PDLC-microprism enables the tuning of radiation pattern when applying voltage. The lighting chip with PDLC-microprism has the following advantages, (1) no moving parts are required to tune the radiation pattern, (2) the shape of PDLC-microprism array can be easily changed by molding processes, and (3) the fabrication and packaging are performed at low temperature and the damage to PDLC is prevented.

Novel concave-based micro optical components

This research demonstrates three novel concave-based micro optical components. A double-concave (DCV) lens is realized by a simple polymer dispensing and sucking process. The DCV component consists of a high-aspect-ratio lens frame structure and dispensed UV-curable polymer lens. Moreover, this study further employs the process for DCV to implement the concave-mirror and the doublet. The measurements show a typical DCV (made of NOA63 polymer) has negative focal lengths of -1.42 mm (for 632.8 nm red-laser) and -1.17 mm (for 473 nm blue-laser), and a typical concave mirror has a focal-length of 3.28mm. The NOA63/PDMS doublet is also demonstrated.

Formation and curvature tuning of micro lens using surface tension and hydraulic pressure assisted molding process

This study presents a novel concept for the formation of curvature micro lens and the lens-curvature tuning using the hydraulic pressure and surface tension assisted molding process. The liquid UV-curable polymer is defined by hydraulic pressure, surface tension, and molding, and then solidified by UV-light to form t he micro-lens. Merits of the process technology are: (1) initial lens curvatures defined by the polymer volume and surface tension, (2) final lens curvature is tuned by the hydraulic pressure, and (3) optical pattern (Fresnel zone) can be defined by molding. In applications, the biconvex, biconcave, and convex-concave lens, and the curved Fresnel lens are demonstrated. The lens radius of curvature Rc is varying from -0.58mm to 1.5 mm. The integration of micro-lens with magnet holder for actuation is also demonstrated.

Design and implementation of an on-chip polymer micro ball bearing

This study presents a novel design and fabrication process to realize an on-chip micro ball bearing. The ball bearing consists of a polymer-Si-polymer outer-race (stator), and a suspended polymer-Si-polymer inner-disk (rotor) supported by polymer micro-balls. The outer-race and inner-disk are demolded from silicon mold, which is patterned by wet isotropic etching on double-polished 525 μm-thick silicon wafer. The liquid phase photocurable polymer balls are dispensed by commercial dispenser with a hundred micrometer diameter tip and in-situ self-assembled in buffer liquid. After photocurable polymer solidified by UV-curing, the polymer balls are confined between the outer race and inner disk. Note the ball bearing is fabricated on a single wafer with no assembly required.

Development of passive and active microprism arrays to change the radiation pattern of solid-state lighting

This study implements a compact solid-state lighting chip with changeable illumination map as well as radiation pattern. The lighting chip consists of a microprism array, light-emitting diode (LED) chip and Si carrier. The polydimethylsiloxane (PDMS) and polymer-dispersed liquid crystal (PDLC) layers are respectively employed to implement the passive and active microprism arrays. The specific radiation pattern can be defined by the shape of the passive PDMS-microprism. Moreover, by using the scattering and transmitting modes of the PDLC layer, the PDLC-microprism enables the changing of light shaping by applying voltage. Thus, the radiation pattern can be changed by the driving voltage on the PDLC layer, and the deformable and movable micro optical components are not required. This study has established the low-temperature fabrication and packaging processes to realize the lighting chip, and the damage of the PDMS and PDLC material is prevented. Typical dimensions of the PDMS lighting chip are 5 mm wide, 6 mm long and 1 mm thick, and The PDLC lighting chip is 550 µm thick. The measurement results show that the PDMS-microprism array can change the radiation pattern from a 70° half-maximum viewing angle to 52° and 40° half-maximum viewing angles on two orthogonal axes. In addition, the PDLC-microprism array can change the radiation pattern from 51° and 43° half-maximum viewing angles at 0 V (i.e. scattering mode) to 48° and 33° half-maximum viewing angles at 100 V (i.e. transmitting mode).