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![Deep Reactive Ion
Etching(DRIE)
Fabrication technology used to create high- aspect
ratio microstructures.
Highly anisotropic etch process used to create deep
penetration, steep-sided holes and trenches in wafers.
Two main technologies for high-rate DRIE: cryogenic and
Bosch. Both processes can fabricate 90° (truly vertical)
walls.
In cryogenic-DRIE, the wafer is chilled to −110°C.The low
temperature slows down the chemical reaction that produces
isotropic etching. It produces trenches with highly vertical
sidewalls.
In Bosch, a standard isotropic plasma etch is done. The
plasma contains some ions, which attack the wafer from a
nearly vertical direction. Sulfur hexafluoride[SF6] is often
used for silicon. Deposition of a chemically
inert passivation layer is also done alternately.](https://image.slidesharecdn.com/opticalmems-150404105937-conversion-gate01/75/Optical-MEMS-14-2048.jpg)
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Optical MEMS
- 1. Welcome to Seminar on OPTICALMEMS Name of Guide Name-Anisha Singhal Prof. R.S. Meena Roll No.-11/278
- 2. MEMS Acronym forMicroelectromechanical Systems Consist of mechanical microstructures, microsensors, microactuators and microelectronics, all integrated onto the same silicon chip. Have the ability to sense, control and actuate on the micro scale, and generate effects on the macro scale. Have the feature size in the range of 1μm-1mm. Advantages: low weight, low cost, low energy consumption, quick response time, high resolution and high sensitivity.
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- 4. Optical mems Fusion ofthree technologies
- 5. Why mems usedin optics The wavelength of light is in the µm range as the MEMS smallest features. Micro-forces generated by micro-actuators have no difficulty in acting on mass less photons. A photon has no mass, so easy to deflect light. Miniature optical elements capable of moving and managing light. Directly manipulate an optical signal eliminating unnecessary optical-electrical-optical (O-E-O) conversions. The effect of moving optical elements is stronger than electrooptic, thermal-optic effects Very efficient beam steering devices can be made.
- 6. Fabrication Silicon isdominant material for fabrication. Conventional IC processes (lithography, depositions, implantation, dry etching, etc.) are often used in microstructure formation. Micromachining is the process of shaping silicon or other materials to realise 3-D mechanical structures in miniature form and the mechanical devices that are compatible with the micro electronic devices.
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- 8. Bulk Micromachining Forrealization of 3D optomechanical structures on Si substrate for aligning optical fibers or forming optical MEMS devices. Single Crystal Silicon is used as the basic material. The process impacts the substrate. Use either wet or dry anisotropic etching (or both). With SOI wafers, a thin top layer of single crystal silicon (50um—100 um) is separated from a larger silicon substrate by a thin oxide layer which serves as an etch stop and a microstructure release mechanism. Many liquid etchants demonstrate dramatic etch rate differences in different crystal directions. <111> etch rate is slowest, <100> and <110> fastest.
- 9. Anisotropic Etching ofSilicon • Anisotropic etches have direction dependent etch rates in crystals . • Typically the etch rates are slower perpendicularly to the crystalline planes with the highest density. • Commonly used anisotropic etches in silicon include Potasium Hydroxide (KOH), Tetramethyl Ammonium Hydroxide (TmAH), and Ethylene Diamine Pyrochatecol (EDP) . <111> <100> Silicon Substrate 54.7
- 10. Surface Micromachining Depositionand etching of different structural layers on top of the substrate. Structural Layer has the desired electrical, mechanical and thermal properties. Polysilicon is commonly used as one of the layers. Sacrificial layer supports the structural layer until it is etched- during ‘release etch’. Silicon dioxide is used as a sacrificial layer which is removed or etched out to create the necessary void in the thickness direction. Surface micro-machining leaves the wafer untouched, but adds/removes additional layers above the wafer surface.
- 11. Surface Micromachining Deposit sacrificiallayer Pattern contacts Deposit/pattern structural layer Etch sacrificial layer
- 12. Lithographie, Galvanoformung, Abf ormung (LIGA)Fabrication technology used to create high- aspect ratio microstructures. Consists of three main processing steps: lithography, electroplating and molding. Polymethyl methacrylate (PMMA) is applied as photoresist to the substrate by a glue-down process. Two main types of LIGA Technology: X-ray LIGA and Extreme Ultraviolet (EUV) LIGA. X-ray LIGA can fabricate with great precision high aspect ratio microstructures whereas EUV LIGA can fabricate lower quality microstructures. Deposition of adhesion, seed layer and photoresist is done in lithography process and then it is exposed to the synchrotron radiation Electroplating is a process to fill in the voids between the polymeric features. Molding is process of machining the overplated region filling the microstructure.
- 14. Deep Reactive Ion Etching(DRIE) Fabrication technology used to create high- aspect ratio microstructures. Highly anisotropic etch process used to create deep penetration, steep-sided holes and trenches in wafers. Two main technologies for high-rate DRIE: cryogenic and Bosch. Both processes can fabricate 90° (truly vertical) walls. In cryogenic-DRIE, the wafer is chilled to −110°C.The low temperature slows down the chemical reaction that produces isotropic etching. It produces trenches with highly vertical sidewalls. In Bosch, a standard isotropic plasma etch is done. The plasma contains some ions, which attack the wafer from a nearly vertical direction. Sulfur hexafluoride[SF6] is often used for silicon. Deposition of a chemically inert passivation layer is also done alternately.
- 16. ACTUATORS Converts electricalsignals to mechanical displacements of mirrors. A type of motor that is responsible for moving or controlling a mechanism or system. It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion.
- 17. Electrostatic Actuation Voltage isapplied between the movable and the fixed electrodes. The moving part rotates about the torsion axis until the restoring torque and the electrostatic torque are equal.
- 18. Magnetic Actuation Theprinciple of magnetic actuation is based on the Lorentz Force Equation. Magnetic field can be induced by electrical current which can generate the force exerted on the moving magnetic material. Electromagnetic coils can be integrated on the movable part, making it quasi- magnetic by current injection. Can operate in liquid environment.
- 19. Thermal Actuation Themismatch between thermal expansion coefficients of materials yields structural stress after temperature change. Generates motion by thermal expansion amplification. A small amount of thermal expansion of one part of the device translates to a large amount of deflection of the overall device. The structure deforms due to this built-in stress. Ability to generate large deflection. Microfabricated thermal actuators can be integrated into micromotors.
- 20. Digital micromirror devices(DMD) Array of tiny mirrors (up to 2 million). Each mirror pivots about a fixed axis. Each mirror acts as a digital light switch ◦ ON: Light is reflected to desired target ◦ OFF: Light is deflected away from target Pulse Width Modulation (PWM) techniques are used to perform digital light modulation. 1024 shades of gray and 35 trillion colors possible. Used in projection systems(Digital Light Processing (DLP) projectors), TV and theaters.
- 21. DMD Specifications MirrorSize = 16µm x 16µm Resonant Frequency = 50kHz Switching Time < 20µSec Total Rotational Angle = 10° Total Efficiency of Light Use > 60% Fill Factor per Mirror = 90%
- 23. Mirror mounting mechanism Each mirror is mounted on Hinge Support Posts. Each mirror rotates about the posts. Torsion hinge restores the mirror to its default horizontal state when no power is applied to the circuit.
- 24. Mirror Rotation Eachmirror rotates ±10° for total rotational angle of 20° Landing Electrode provides stop pad for the mirror and allows precise rotational angles.
- 25. Bias Bus &Address Electrodes Bias/Reset Bus provides stop pad and connects all mirrors to allow for a bias/reset voltage waveform to be applied to the mirrors Address electrodes are connected to an underlying SRAM cell’s complimentary outputs
- 26. SRAM Cell ComplimentarySRAM cell outputs connected to the address electrodes actuate the mirrors by electrostatically attracting/repelling the free corners of the voltage-biased mirrors.
- 27. Principle of Operation Balancingelectrical torque with mechanical torque Telectrical is proportional to (voltage)2 Tmechanical is proportional to (deflection, a) a
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- 29. OPTICAL SWITCHING Switchingis the process by which the destination of an individual optical information signal is controlled. A micro-mirror is used to reflect a light beam in MEMS optical switch. The direction in which the light beam is reflected can be changed by rotating the mirror to different angles, allowing the input light to be connected to any output port. Realized through the fusion of various techniques such as micro- machining techniques for fabricating the mirror, optical design techniques for achieving low-loss optical connections, and control techniques for positioning the mirror accurately. Can switch large numbers of optical signals simultaneously. It can be used as a trunk switch for handling large amounts of traffic, and as a switch in large urban communication networks.
- 30. High bitrate transmission must be matched by switching capacity. Switching can be performed in 10-30 msec. Optical or Photonic switching can provide such capacity. Can switch optical signals without converting them into electrical signals. CURRENT 64 kbits/sec for each subscriber (1 voice channel) Estimated aggregate switching capacity is 10 Gbits/sec PROJECTED 155 Mbits/sec for each subscriber (Video + data etc..) Estimated aggregate switching capacity is 15.5 Tbits/sec Example: 100,000 subscriber digital exchange The need for Optical Switching
- 31. Why optical switches Increasingnumber of wavelengths and bandwidth in dense wavelength-division-multiplexed (DWDM) networks enhanced its need. Explosive network traffic Rapidly growing data rate and port count Bottleneck due to conventional OEO switches (bandwidth, bit error rate and capacity mismatch). Cost effective
- 32. 2D MEMS Switches Mirrors have only 2 positions (cross or bar) Crossbar configuration N2 mirrors
- 33. Mirrors requirecomplex closed-loop analog control But loss increases only as a function of N1/2 Higher port counts possible. Mirrors can be tilted to any angles N or 2N mirrors accomplish non-block switching. Good scalability 3D MEMS based Optical Switch Matrix
- 34. Fastest Optical Switch Switch-on and switch-off a semiconductor optical cavity within a world-record short time of less than 1 picosecond. Ultrafast optical data communication. Tiny on-chip light sources and lasers. Cavities are used for their ability to store light in a volume in space for a particular duration of time. A generic cavity consists of two mirrors separated by a length of transparent material. In the cavity, light bounces back and forth between the mirrors. Light is an electromagnetic wave, so only waves whose wavelength (or color) matches the cavity length can exist in the cavity Constructive interference where crests and valleys of many waves coincide, and therefore add up to a high intensity. As a result, the allowed waves resonate to form a standing wave in the cavity.
- 35. When white lightis sent to the cavity only blue light constructively interferes inside and is transmitted. This situation defines a "zero" bit. When control (indicated by green star) and signal light pulses arrive at the same time, the cavity is switched by the control light. As a result, red light is transmitted through the cavity. This defines a "one" bit. Later the situation returns to the starting situation.
- 36. Advantages of opticalmems Offer more than 10 terabits per second of total switching capacity, with each of the channels supporting 320GB per second which is 128 times faster than current electronic switches. Nearly 32 times denser than an electronic switch. Low optical insertion loss, low crosstalk and low power consumption. Transparency (wavelength, polarization, bit rate, data format). Cost effective wafer scale manufacturing. Use of Si fabrication technology results in stiffer mirrors that are less prone to drifting out of alignment and which are robust, long lived and scalable to large no. of devices on wafer.
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- 38. Conclusion This newtechnology has the potential to revolutionize the optical components industry. MEMS optical switches are currently dominant and promising in the future. Bit rate independent, MEMS based optical components will “future proof” next generation networks. Optical MEMS accelerate deployment of the “all optical network”.