Microshutter Arrays Research Articles

A MEMS Electrostatic Roll-Up Window Shade Array for House Energy Management System

We report on an electrostatically reconfigurable roll-up microshutter array by using the mechanical unimorph effect of laminated metal-SiO2 microcantilevers. The shutter array is designed as a tunable shade to control the incoming sunlight through windows. Materials and fabrication are chosen to be in compatible with the thin-film-transistor technology for electrically addressing. The shutter is 200- $\mu \text{m}$ long, 30- $\mu \text{m}$ wide, and 0.3- $\mu \text{m}$ thick. The radius of the shutter curvature is 70 $\mu \text{m}$ , which is quantitatively predictable by Timoshenko’s model for the unimorph structure. The shutter is electrostatically closed at 55 V and released at 38 V to, respectively, switch the mechanical aperture between 0% and 55%. Optical transmittance is controlled between 36% (close) and 53% (open).

2-D Electrostatic Actuation of Microshutter Arrays

Electrostatically actuated microshutter arrays consisting of rotational microshutters (shutters that rotate about a torsion bar) were designed and fabricated through the use of models and experiments. Design iterations focused on minimizing the torsional stiffness of the microshutters while maintaining their structural integrity. Mechanical and electromechanical test systems were constructed to measure the static and dynamic behavior of the microshutters. The torsional stiffness was reduced by a factor of four over initial designs without sacrificing durability. The analysis of the resonant behavior of the microshutters demonstrates that the first resonant mode is a torsional mode occurring around 3000 Hz. At low vacuum pressures, this resonant mode can be used to significantly reduce the drive voltage necessary for actuation requiring as little as 25 V. The 2-D electrostatic latching and addressing was demonstrated using both a resonant and a pulsed addressing scheme. [2015–0172]

GESE: a small UV space telescope to conduct a large spectroscopic survey of z∼1 Galaxies

One of the key goals of NASA’s astrophysics program is to answer the question: How did galaxies evolve into the spirals and elliptical galaxies that we see today? We describe a space mission concept called Galaxy Evolution Spectroscopic Explorer (GESE) to address this question by making a large spectroscopic survey of galaxies at a redshift, z∼1 (look-back time of ∼8 billion years). GESE is a 1.5-m space telescope with an ultraviolet (UV) multi-object slit spectrograph that can obtain spectra of hundreds of galaxies per exposure. The spectrograph covers the spectral range, 0.2–0.4 μm at a spectral resolving power, R∼500. This observed spectral range corresponds to 0.1–0.2 μm as emitted by a galaxy at a redshift, z=1. The mission concept takes advantage of two new technological advances: (1) light-weighted, wide-field telescope mirrors, and (2) the Next-Generation MicroShutter Array (NG-MSA) to be used as a slit generator in the multi-object slit spectrograph.

Microshutter arrays will paint the picture of the early universe

Microshutter arrays will paint the picture of the early universe

Response of a MEMS Microshutter Operating at 60 K to Ionizing Radiation

Total ionizing dose (TID) measurements at low temperature (60 K) of a micro-electro-mechanical system (MEMS) microshutter array (MSA) indicate that exposing the MSA to ionizing radiation causes some of the shutters to stop operating properly. The number of non-functional shutters depends on the applied bias. With increasing dose, the number of micro-shutters that become non-functional increases.

Cryogenic characterization and testing of magnetically-actuated microshutter arrays for the James Webb Space Telescope

Two-dimensional MEMS microshutter arrays (MSA) have been fabricated at the NASA Goddard Space Flight Center (GSFC) for the James Webb Space Telescope (JWST) to enable cryogenic (∼35 K) spectrographic astronomy measurements at near-infrared wavelengths. Functioning as a focal plane object selection device, the MSA is a 2D programmable aperture mask with fine resolution, high efficiency and high contrast. The MSA are close-packed silicon nitride shutters (cell size of 100 µm × 200 µm) patterned with a torsion flexure to allow their opening to 90°. A layer of magnetic material is deposited onto each shutter to permit magnetic actuation. Two electrodes are deposited, one onto each shutter and another onto the support structure side-wall, permitting electrostatic latching and 2D addressing. New techniques were developed to test MSA under mission-similar conditions (8 K ⩽ T < 300 K). The ‘magnetic rotisserie’ has proven to be an excellent tool for rapid characterization of MSA. Tests conducted with the magnetic rotisserie method include accelerated cryogenic lifetesting of unpackaged 128 × 64 MSA and parallel measurement of the magneto-mechanical stiffness of shutters in ‘pathfinder’ test samples containing multiple MSA designs. Lifetest results indicate a logarithmic failure rate out to ∼106 shutter actuations. These results have increased our understanding of failure mechanisms and provide a means to predict the overall reliability of MSA devices.

Arrays of addressable contactless optical microshutters

The present paper describes the development of contactless optical microshutter arrays, which are mounted in an assembly of microlenses, optical fibers and driving electronics. In the past, complete systems have been made, for different applications, by using microshutters with contacting surfaces. We have been able to demonstrate the functionality of these complete devices, but in-use stiction limited their lifetime. The arrays also showed short-circuit due to shutters jumping over the electrodes, because of an asymmetrical electrical field distribution.Despite years of advancements in micromachining technologies, in-use stiction remains a fundamental issue in micro electro-mechanical systems (MEMS), resulting in device failure. Anti-stiction layers have been developed and even industrialized, but they require hermetically sealed devices or have a limited lifetime. A more drastic solution to solve in-use stiction and jump over is to resort to a device without any mechanical stopper. After having considered several solutions, we have designed, manufactured and successfully tested contactless shutters.

An electrostatic actuator for fatigue testing of low-stress LPCVD silicon nitride thin films

An electrostatic actuator and mechanical-amplifier (MA) device has been designed and fabricated to study fatigue properties of low-stress LPCVD silicon nitride thin films. The device consists of two resonators connected serially with a common torsion bar. When pumping electrostatic energy into the first resonator, the energy is transferred to the second resonator via the common torsion bar. The mechanical movement of the second resonator is thus amplified, introducing high stress levels (up to 7.7 GPa) when actuated at its first resonant mode. All devices were tested inside a focused-ion-beam (FIB) system with pressure of 10 −6 Torr at room temperature (23 ± 1 °C), and the test duration ranged from 5 s to 8.5 h, 10 5 to 10 9 cycles, respectively. An ANSYS finite-element-analysis (FEA) model was built to determine the maximum operating stress of the devices. From the experiment, no failure of low-stress LPCVD silicon nitride thin films has been found even up to 10 9 cycles when testing at stress amplitude below 5.8 GPa with a load ratio of 0.03. The presented device design and experimental technique can be used to characterize fatigue properties of different microelectromechanical systems (MEMS) materials, and the test results are utilized in the design of microshutter arrays, programmable field selectors in the NASA James Webb Space Telescopes (JWST).

A cryogenic measurement setup for microelectromechanical systems used in space applications

We present a cryogenic measurement setup installed inside a focused-ion-beam (FIB) system to characterize and microrepair microelectromechanical systems (MEMS) for space applications. The setup allows testing of MEMS devices under vacuum condition of 10−6Torr at variable temperatures ranging from 298to20K. In the experiment, a lead-zirconate-titanate translator powered by a function generator and a dc voltage is utilized as an actuator, and a thin-film thermo-resistor fabricated with test devices is used as an integrated temperature sensor. Additionally, a motorized x-y-z stage is installed to achieve highly accurate positioning function. Resonant techniques and bending tests based on the designed setup are developed to measure the mechanical properties of silicon nitride thin films at cryogenic temperatures. Combined with the functions of the FIB system, this setup also demonstrates the capability to microrepair microshutter arrays, programmable field selectors in the NASA James Webb Space Telescopes. The presented test setup exhibits its feasibility to test MEMS devices needed for the space applications and can be extended to other cryogenic applications.

Programmable Microshutter Arrays for the JWST NIRSpec: Optical Performance

Two-dimensional microshutter arrays (MSAs) are being developed at the NASA Goddard Space Flight Center for the James Webb Space Telescope (JWST) for use as a programmable aperture mask for object selection for the Near Infrared Multiobject Spectrograph (NIRSpec). The MSAs are designed to provide high transmission efficiency for the selected objects and high on to off contrast ratio at the /spl sim/35 K operating temperature of JWST. The arrays of shutters are produced from silicon nitride membranes on a 100/spl times/200 /spl mu/m pitch. Individual shutters consist of a shutter blade of silicon nitride suspended from the shutter frame by a nitride torsion flexure. The shutters are normally closed. All shutters in the array are opened by the scanning magnetic field, and are held open by an electrostatic potential applied between the open shutters and the shutter support grid electrodes. To close the required shutters for a specific configuration, the potential between the shutter to be deselected and the support frame is set to zero, allowing the shutter to close. In this way, full random access addressing is achieved. We have produced such shutters and have demonstrated mechanical actuation and selection. Optical tests of open and closed shutters have demonstrated the required contrast for the JWST application. The MSA is a pioneering technology that provides the most capable possible multiobject spectrograph for JWST. It provides high contrast selection, high transmission efficiency, and can meet the environmental requirements for JWST.

FIB-Based Fatigue Testing of Silicon Nitride Thin Films for Space Applications

ABSTRACTA novel micro-scale electrostatic actuator has been designed and fabricated to study fatigue properties of low-stress LPCVD silicon nitride thin films, which are the structural materials of microshutter arrays to be used in NASA's James Webb Space Telescope (JWST). To obtain different stress levels without high applied voltages, the electrostatic actuator was designed based on a resonant technique to achieve mechanical amplification. All fabricated devices were tested inside a focused-ion-beam (FIB) system with pressure of 10-6 torr at room temperature (23 ± 1 °C) and with the test duration ranging from 5 seconds to 8.5 hours, 105 to 109 cycles, respectively. From the experiment, no fatigue failure of low-stress LPCVD silicon nitride thin films has been observed up to 109 testing cycles, four orders of magnitude higher than the expected lifetime of the microshutter arrays. The presented test device and experimental technique can be extended to characterize fatigue properties for other thin film materials.