Finally, 50 ��m thick SU8 was spun onto the mold, exposed, and cross-linked slowly from 60-90��C for 1.5 hrs. The resultant SU8 lens had a refractive index of 1.6 with curvature calculated by volume conservation before and after the reflow. The PDMS layer was then subsequently removed. The final structure was a robust, cured-epoxy diaphragm-suspended microlens with controlled curvature (Figure 2b).Microspectrometer AssemblyThe MEMS grating and fiber input components were fabricated separately. To package the lens with wafer-level encapsulation, multilayers of silicon substrates with cavity geometries were fabricated. The individual silicon substrate layers were fabricated by KOH bulk microfabrication. First, 7,000 ? thick layer SixNy thin film was deposited by low pressure chemical vapor deposition (LPCVD).

Etch windows were then transferred to this thin film via lithography and CF4 reactive ion etching (RIE). KOH at 89��C provided the anisotropic etching through these windows to form the cavities. One of the four layers depicted in Figure 3 housed the microlens diaphragm, whose process was described in the preceding section. The bottom most layer contained the MEMS actuator, also processed separately. The four layers were aligned and bonded in the next step.Figure 3.(a) Multi-layer silicon cavity packaging of microlens and other MEMS components of the micro-spectrometer. (b) The 5 mm by 5 mm package with cross-section (top) and perspective (bottom) view.After removing nitride diaphragms via ultrasonication, the wafers were handled within a contact aligner (MJB3, Karl-Suss) for aligned epoxy bonding.

One wafer was fixed onto a glass plate by capillary force with controlled amount of water. The other wafer was then spun with premixed epoxy and quickly transferred to the aligner for aligning and contact bonding. When the wafers were aligned, they were brought to contact by physical force and securely seated. In addition to this aligned bonding, the layer containing silicon micromirror was coated with evaporated aluminum (1,000 ?) to enhance reflectivity, with oxygen plasma cleaning to remove excess epoxy.This bonded optical subsystem was diced to individual unit dies of 5 mm by 5 mm. However, dicing was carried out to leave 80 ��m of thickness to allow wafer AV-951 handling prior to encapsulating the MEMS components.

The MEMS components were partially diced just as in packaging, released via RIE in CF4 plasma, and align bonded to the SSC encapsulation with epoxy. The resultant wafer level package could be separated by breaking the partially diced wafers by hand (Figure 3b).3.?Microlens Characterization by Gaussian Beam PropagationMicrolens focusing is a Gaussian transformation. When combined with the resolving power of the microspectrometer’s grating, it produces a linear dispersion that critically affects the overall system resolution.