PROCEEDINGS ARTICLE | August 30, 1999
Proc. SPIE. 3874, Micromachining and Microfabrication Process Technology V
KEYWORDS: Infrared bolometers, Infrared sensors, Sensors, X-rays, Silicon, Computer simulations, Scanning electron microscopy, Detector arrays, Structural design, Semiconducting wafers
High sensitivity is a basic requirement for a new generation of thermal detectors. To meet the requirement, close-packed, 2D silicon detector arrays have been developed in NASA Goddard Space Flight Center. The goal of the task is to fabricate detector arrays configured with thermal detectors such as IR bolometers and x-ray calorimeters to use in space flight missions. This paper focuses on the fabrication and the mechanical testing of detector arrays in a 0.2 mm pixel size, the smallest pop-up detectors being developed so far. These array structures, nicknamed 'PUDs' for 'Pop-Up Detectors', are fabricated on 1 micrometers thick, single-crystal, silicon membranes. Their designs have been refined so we can utilize the flexibility of thin silicon films by actually folding the silicon membranes to 90 degrees in order to obtain close-packed 2D arrays. The PUD elements consist of a detector platform and two legs for mechanical support while also serving as electrical and thermal paths. Torsion bars and cantilevers connecting the detector platform to the legs provide additional flexures for strain relief. Using micro- electromechanical structure fabrication techniques, including photolithography, anisotropic chemical etching, reactive-ion etching, and laser dicing, we have fabricated PUD detector arrays of fourteen designs with a variation of four parameters including cantilever length, torsion bar length and width, and leg length. Folding test were conducted to test mechanical stress distribution for the array structures. We obtained folding yields and selected optimum design parameters to reach minimal stress levels. Computer simulation was also employed to verify mechanical behaviors of PUDs in the folding process. In addition, scanning electron microscopy was utilized to examine the flatness of detectors and the alignment of detector pixels in arrays. The fabrication of thermistor and heaters on the pop-up detectors is under way, preparing us for the next step of the experiment, the thermal test.
