microshutters for particle velocity measurements: modelling and fabrication klas brinkfeldt swedish...

Microshutters for particle velocity measurements: Modelling and fabrication

Klas Brinkfeldt

Swedish National Graduate School of Space Technology Workshop, ESTEC, Sept 13-15 2006

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.




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.


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.




Shutter design

Parameter ValueOpen time, t 25 nsClosed time, t 1700 nsDriving frequency, f 300 kHzTransparency, > 10 -5

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.



Shutter design

tf

t 2

1 12384

3

3

hbE

Fly

2

2

0 2d

AVF

ModelModel

DesignDesign

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

vmax

t

A dynamic model of an opening in a oscillating layer moving over a static layer is used to find the required oscillation amplitude.

ftydt

dv 2sin

max

2

v

st

Optimization


105 m

105 m

10 m90 m

5 m85 m

60 m

20 m


Shutter design



SimulationsSimulations 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



Fabrication


Photoresist

UV

SiO2

Si substrate

From pattern to 3D-structure

1.) Wafer preparation

2.) Photolithography

3.) Remove exposed photoresist

4.) Oxide etch

5.) Silicon etch


Fabrication

Bondpads

Moving plates

1 micron slits Electrostatic drivers Via connection

Static Device (SD)

Static Handle (SH)

Dynam ic Handle (DH)

Dynam ic Device (DD )

S ilicon

O xide

A l

R esist

A

B

• 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.


• 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.



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 Flixel TMOS optical from University of Washington James Webb Space Telescope by the NASA Goddard Space Flight Center.


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.


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 2008.

• 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.


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


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.


MEMS shutter design

Based on resonant vibrations of a grated moving layer in between two static layers.

Static

Static

Parameter ValueSensor specificationsEnergy resolution,E/E, % 7Mass resolution,M/M, % 20Mass (min), amu 1Mass (max), amu 32Energy (min), eV 50Energy (max), eV 10000TOF distance, cm 3.8

TOF specificationsTOF (min), ns 28TOF (max), ns 2204

Shutter characteristicsFrequency (min), KHz 227Open time (max), ns 2.62Transperancy (max) 1.85E-03Duty cycle 1.19E-03Efficiency 2.20E-06


MEMS shutter design

Attached to fixed frame

}SOI wafer

}Bonded wafer

Moving layer

Passivly closed(not aligned withdevice layer)

1 m opening

1 m opening

5m opening

Fixed electrode

1 m

80 m

30 m

Opening slits dimensions of SOI waferReleased plate

SOI device layer thickness = 10 m

Complicates process


105 m

105 m

10 m90 m

5 m85 m

60 m

20 m


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


Contact


microshutters for particle velocity measurements: modelling and fabrication klas brinkfeldt swedish...

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