Microshutters for particle velocity measurements: Modelling and fabrication Klas Brinkfeldt Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept Swedish Institute of Space Physics, Kiruna

The Swedish Institute of Space Physics (IRF) Department of Microtechnology and Nanosciences, Chalmers University of Technology Solar System Physics and Space Technology group at IRF: Conducts comparative research on the evolution and dynamics of the solar system objects and their interaction with the solar wind. Manufacture ion mass spectrometers, electron spectrometers, energetic particle detectors, and energetic neutral atom (ENA) imagers to study Mercury, Venus, Earth, Mars, and comets. Solid State Electronics group at MC2: Specializes on silicon and silicon related materials and devices including: - MOS (Metal-Oxide-Semiconductor) physics and devices. - Wafer bonding and SOI technology. - Substrate Noise Coupling in Mixed-Signal System-on- Chip. - Transistors. - Micro- and Nanosystems. Microshutters for particle velocity measurements: Modelling and fabrication Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

Microshutters for particle velocity measurements: Modelling and fabrication Mass spectrometers for space particle measurements: Time of flight (TOF) systems Particle pass through foil or graze surface. Electrons emitted in the interaction are collected to produce a START signal.The original particle continues across a defined distance to a second detector generating a STOP signal. The time between START and STOP is measured and the velocity can be calculated. Particles lose part of its energy in the foil/surface interaction. Particles lose direction in the foil/surface interaction. Cannot measure low energy neutrals. Magnetic mass identification systems Particle energy is determined in an electrostatic analyzer (ESA). Particle mass can then be determined by measuring the particle deflection in a known magnetic field. Generally requires large volume. Heavy permanent magnets. Lower signal to noise ratios. Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

Shutter based velocity measurements Mechanical velocity determination (rotating disc system) was attempted on sounding rocket experiments in the 1970s [Moore Jr. et al. 1975]. Large mass, high power consumption and high torque it would exert on spacecraft made them impossible to use on satellites. With micromechanics the idea can now work. Microshutters for particle velocity measurements: Modelling and fabrication Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

Microshutters for particle velocity measurements: Modelling and fabrication Shutter design ParameterValue Open time,  t25 ns Closed time, t1700 ns Driving frequency, f300 kHz Transparency,  > Main objectives: 1.Develop and manufacture a MEMS shutter for applications in space particle instruments and 2.verify its performance in the miniature ion spectrometer PRIMA. The design requirements are a result of: Expected ion flux based on previous measurements. PRIMA parameters. Target resolution of the measurements. Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

Microshutters for particle velocity measurements: Modelling and fabrication Shutter design Model Design F A stress and strain model is used to find the force required to actuate the plate structures. f Static layer Oscillating layer Open t y v max t A dynamic model of an opening in a oscillating layer moving over a static layer is used to find the required oscillation amplitude. Optimization Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

105  m 10  m 90  m 5  m 85  m 60  m 20  m Microshutters for particle velocity measurements: Modelling and fabrication Shutter design Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

Microshutters for particle velocity measurements: Modelling and fabrication Simulations Simulations using COMSOL (v3.2) to find: 1.Eigenfrequency of the desired oscillation mode including: Effects of the opening slits in the plates. Effects of the comb actuation fingers. 2.Driving voltage to generate the displacement required. 3.Stress generated in the beams. 4.Required frame dimensions to minimize coupling between different shutter elements. f = 306 kHz f = 279 kHz f = 285 kHz f = 306 kHz Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

Microshutters for particle velocity measurements: Modelling and fabrication Fabrication Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept Photoresist UV SiO 2 Si substrate From pattern to 3D-structure 1.) Wafer preparation 2.) Photolithography 3.) Remove exposed photoresist 4.) Oxide etch 5.) Silicon etch

Microshutters for particle velocity measurements: Modelling and fabrication Fabrication First batch of prototype microshutters currently under fabrication. The process requires 9 masking steps. Bonding of two SOI (Silicon on Insulator) wafers together at the device layers. Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept Wafer is divided in 55 chips (10 mm × 10 mm). Each chip contains an array of hundreds of microshutters.

Summary Shutter based mass spectrometry. Possibility to measure low energy neutral particles (for example, particles sputtered from the surfaces of Mercury or the Moon). Immunity to contamination from UV photons. More compact systems (less volume and mass). Improved resolution (no particle interaction to generate a START signal). MEMS technology shutters are under development. An optimized prototype design from theory. Simulations have been used to verify the model. Fabrication is in progress. Microshutters for particle velocity measurements: Modelling and fabrication Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept

Advantages of shutter based velocity measurements Dramatically improved resolution (no particle interaction to generate a START signal). Possibility to measure low energy neutral particles (for example, particles sputtered from the surfaces of Mercury or the Moon). Immunity to contamination from UV photons. More compact systems (less volume and mass). ”Flipping pixel” system by FlixelTMOS optical from University of Washington James Webb Space Telescope by the NASA Goddard Space Flight Center. Microshutters for particle velocity measurements: Modelling and fabrication

The LEIA (Low Energy Ion Analyzer) project Main objectives: 1.Develop and manufacture the first ever MEMS shutter for applications in space particle instruments and 2.verify its performance in the LEIA instrument to fly onboard the Swedish technological satellite PRISMA and/or other flight opportunities. Microshutters for particle velocity measurements: Modelling and fabrication

LEIA Flight opportunities PRISMA Satellite - Technology mission to verify autonomous formation flying (Guidance, Navigation, and Control, GNC) for future European space missions. - Consists of two spacecraft, MAIN and TARGET, that will demonstrate rendezvous and coarse formation flight. Swedish Space Corporation (SSC) main contractor along with German and French space agencies. - Launch with Russian ”Dnepr” rocket into a polar Earth orbit in the second half of Sounding rocket from ESRANGE - ESRANGE launches several rockets year of different sizes. To place LEIA on board we need formal approval of the main experiment on board (buyer of the launch). - Sounding rockets do not enter Earth orbit. Flight time 10 ~ 15 minutes. - Low altitude 100 ~ 800 km, which may cause saturation problems in LEIA (too many particles). Fregat (final stage on a Russian Soyuz rocket) -Soyuz final stage Fregat completes several orbits after the launched satellite is separated. - Orbit depends on satellite orbit. Microshutters for particle velocity measurements: Modelling and fabrication

LEIA (Low Energy Ion Analyzer) LEIA will be based on an existing miniaturized ion mass spectrometer design SWIM (Solar Wind Monitor) developed for the Indian Chandrayaan-1 mission to the Moon (launch 2008). SWIM characteristics: Energy range ~10 eV – 15 keV Field-of-view 180° × 9 ° Mass ~400 g Power ~1.5 W Microshutters for particle velocity measurements: Modelling and fabrication

LEIA (Low Energy Ion Analyzer) MEMS shutter LEIA will be based on SWIM but with: the START CEM replaced by a MEMS shutter, newly developed high voltage optocouplers, and partly based on “commercial-off-the-shelf” (COTS) components. Microshutters for particle velocity measurements: Modelling and fabrication

MEMS shutter design Based on resonant vibrations of a grated moving layer in between two static layers. Static Microshutters for particle velocity measurements: Modelling and fabrication

MEMS shutter design Attached to fixed frame Fixed electrode 1  m 80  m 30  m Opening slits dimensions of SOI wafer Released plate SOI device layer thickness = 10  m Complicates process Microshutters for particle velocity measurements: Modelling and fabrication

105  m 10  m 90  m 5  m 85  m 60  m 20  m Microshutters for particle velocity measurements: Modelling and fabrication

Pin out (TBC): HV MEMS area A (~200 V) Position sense MEMS area A (<pF) HV MEMS area B (~200 V) Position sense MEMS area B (<pF) Ground Reference C plate 1 Reference C plate 2 TC1A (Thermocouple mounted on MEMS housing or close to) TC1B Microshutters for particle velocity measurements: Modelling and fabrication

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