Direct-write UV-laser microfabrication of 3D structures in lithium-aluminosilicate glass

ABSTRACT The direct-write laser machining technique has been used to process a lithium- alumosilicate glass (FoturanTM) for an applicationwhich requires 3D patterned microstructures. Using two UV laser wavelengths (248nm and 355 nm), microcavities andmicrostructures have been fabricated for the development of microthrusters for attitude and orbit control of a 1kg class (10 cmdiameter) nanosatellite. In addition, experiments have been conducted to defme the processing window for the laser patterningtechnique. The results include a measure ofthe change in Foturan strength after a required program bake cycle plus HF etching ratesas a function ofthe laser repetition rate for the two UV wavelengths. INTRODUCTION Systems studies show that 21st century low-earth-orbiting (LEO) global communications and earth monitoring systems couldutilize constellations ofhundreds to thousands of individual spacecraft'. The feasibility of amassing and replenishing such largeconstellations will depend on the time and cost for manufacturing and launching individual spacecraft. Current spacecraftmanufacturing approaches lead to production and launch schedules which are measured in years with individual spacecraft costsranging from $1 million (a small limited-function LEO satellite) to well over $100 million (an advanced geosynchronouscommunications satellite) per spacecraft. Spacecraft manufacturing needs to become "faster and cheaper" to enable the massively-populated constellations ofthe future. One solution is to design spacecraft that are amenable to automated assembly and mass-production manufacturing techniques. A radical concept now under consideration is The Aerospace Corporation's Nanosatellitewhich leverages the processes and techniques developed by the microelectronics industry. Exploited to advantage are the automation,fabrication and assembly processes to produce a satellite which resembles a lap top computer in size and mass but is far moresophisticated in packaging. In essence, all the standard satellite subsystems, i.e., propulsion, attitude control, communications, etc.,are fabricated onto a series ofwafers which then get stacked to form a sandwich-like structure. Both monolithic and multichipmodule packaging can be used to integrate the electronics, sensors, microactuators and fluid delivery systems required for afunctioning satellite. Figure 1 shows an artist rendering ofthe Nanosatellite based on 10 cm diameter silicon (plus other materials)wafers. Glass, ceramic and polymeric materials are being considered to take advantage oftheir unique material properties2. Systemsengineering studies confirm that a satellite design as shown in Fig. 1 can conduct continuous global store-and-forwardcommunications and cloud-cover observation missions using 500 to 1000 satellites.The feasibility ofthe Nanosatellite to conduct missions beyond that ofjust a communications mailbox (i.e. store-and-forwardcommunications) will depend on the development of a micro propulsion system for attitude and orbit control3. We are developing UVlaser 3D patterning techniques to fabricate microstructures in alumosilicate glass (FoturanTM) to provide rapid microthrusterprototyping capability4. The techniques employ a high repetition rate UV laser and an XYZ microstepper positioner to selectivelyexpose Foturan without using a physical mask. Three dimensional structures can be fabricated by selecting a laser wavelength todefme the absorption depth, and by controlling both the photon dose and the spatial contour of the laser beam near its focus.Experiments at two laser wavelengths (248 nm and 355 nm) resulted in fabrication of mesoscale devices 400 or 1500 microns highhaving microscale structure lO5tips/cm2). The ability to work in glass permits the prototyping of differentmicrothruster types and other spacecraft subsystems. Microthrusters ranging from cold gas nozzles to ion engines will be necessary tomeet the diverse propulsion requirements of future Nanosatellite missions.Person to whom correspondence should be addressed