When it comes to space applications, specifications usually call for the smallest, lightest, most energy efficient and high performing instruments possible. With this in mind, we worked with MPB Communications to enhance its IOSPEC minispectrometer’s performance capability and make it even more attractive for space missions. This basically involved adding a programmable microshutter array to the minispectrometer which allows it to be used in the “Hadamard transform” mode. Our challenge was to find a practical way of producing microshutters that satisfy client specifications.
The approach we recommended to the client used zipping actuators. Each shutter includes a movable element that exhibits a stress gradient intentionally produced during fabrication. The radius of curvature of the movable element is a function of the stress gradient value. The actuator also includes an electrode fabricated on the supporting substrate. When a voltage difference is applied between the movable element and electrode, the resulting electrostatic force attracts the moveable element to the electrode. In practice, the movable element is then “zipped” onto the electrode and at the same time blocks a transparent slit on the substrate surface. Sixteen of these actuators are juxtaposed to constitute an array.
The array has been tested and meets or exceeds all client specifications. Voltage of approximately 110 V is required to close a slit. Response times for slit closure and opening are approximately 2 and 7 ms respectively. In addition, the parallel fabrication process typical of surface micromachining allows production of over 100 arrays per substrate.
An innovative, versatile technology platform
Our approach allows us to build actuators whose structural components may range from microscopic to over a millimeter in length depending on specifications. In addition, because of the stress gradient introduced in the moveable element, structural components are self-assembled and their maximum distance to the substrate may be as much as several hundred micrometers or even a millimeter or more. This is remarkable for monolithic microdevices fabricated by surface micromachining. Thus this versatile, innovative technology platform can be adapted to produce a variety of devices including, for example, shutters, light modulators, variable focus micromirrors, and beam steering micromirrors.