Micro-Opto-Electro-Mechanical-System MOEMS – Micro-Opto-Electro-Mechanical-System EMT496 Dr. Muhammad Mahyiddin Ramli Semester I 2015/16

Course Background CO1: Ability to develop and summarize the basic MEMS and MEOMS fabrication and devices. CO2: Ability to design and compare the different concept of MOEMS sensors and actuators. CO3: Ability to design and recommend the best solution in solving MOEMS application issues. Lab: 5 labs using MEMSPro (L-Edit) & ANSYS. Started 3rd week. PBL – week 13th. Mid-term Exam – week 6th. End-term Exam – week 14th.

Introduction MOEMS – the integration of micro-optical elements, mechanical elements, sensors, actuators, and electronics on a common silicon substrate through micro-fabrication technology. The ability to alter/modulate/modify the path of a light beam. The most common micro-optical elements are those that reflect, diffract or refract light. The basis for this technology is micromachining which involves the manufacture of mechanical structures in the micron to milli-meter range.

Introduction

Scales and Dimension The overview of MEMS

The overview of MEMS Transducer A transducer is a device that transforms one form of signal or energy into another form. The term transducer can therefore be used to include both sensors and actuators and is the most generic and widely used term in MEMS. Sensor A sensor is a device that measures information from a surrounding environment and provides an electrical output signal in response to the parameter it measured. MEMS devices generally overlap several energy domains or do not even belong in any one category. The overview of MEMS

The overview of MEMS Actuator These energy domains include: • Mechanical - force, pressure, velocity, acceleration, position • Thermal- temperature, entropy, heat, heat flow • Chemical - concentration, composition, reaction rate • Radiant- electromagnetic wave intensity, phase, wavelength, polarization reflectance, refractive index, transmittance • Magnetic- field intensity, flux density, magnetic moment, permeability • Electrical - voltage, current, charge, resistance, capacitance, polarization Actuator An actuator is a device that converts an electrical signal into an action. It can create a force to manipulate itself, other mechanical devices, or the surrounding environment to perform some useful function.

The history of MEMS is useful to illustrate its diversity, challenges and applications. The following list summarizes some of the key MEMS milestones [8]. 1958 - Silicon strain gauges commercially available 1959 - "There's Plenty of Room at the Bottom" - Richard Feynman gives a milestone presentation at California Institute of Technology. He issues a public challenge byth offering $1000 to the first person to create an electrical motor smaller than 1/64 of an inch 1961 - First silicon pressure sensor demonstrated   1967 - Invention of surface micromachining. Westinghouse creates the Resonant Gate Field Effect Transistor, (RGT). Description of use of sacrificial material to free micromechanical devices from the silicon substrate. 1970 - First silicon accelerometer demonstrated   1979 - First micromachined inkjet nozzle History of MEMS

Early 1980's: first experiments in surface micromachined silicon Early 1980's: first experiments in surface micromachined silicon. Late 1980's: micromachining leverages microelectronics industry and widespread experimentation and documentation increases public interest. 1982 - Disposable blood pressure transducer 1982 - "Silicon as a Mechanical Material" [9]. Instrumental paper to entice the scientific community - reference for material properties and etching data for silicon. 1982 - LIGA Process 1988 - First MEMS conference 1990’s - Methods of micromachining aimed towards improving sensors. 1992 - MCNC starts the Multi-User MEMS Process (MUMPS) sponsored by Defense Advanced Research Projects Agency (DARPA) 1992 - First micromachined hinge 1993 - First surface micromachined accelerometer sold (Analog Devices, ADXL50) 1994 - Deep Reactive Ion Etching is patented 1995 - BioMEMS rapidly develops 2000 - MEMS optical-networking components become big business History of MEMS

What is optical elements? What is actuators? What is sensor? Is a converter that measures a physical quantity and converts it into a signal which can be read Servomechanism that convert energy into the motion of system. What is optical elements? What is mechanical? A part of an optical instrument which acts upon the light passing through the instrument, such as a lens, prism, mirror. A system that manages power to accomplish a task that involves forces and movement. -chain, belt, gear, linkage.

Con’t Electrical: the study and application of electricity, electronics, and electromagnetism. Optoelectronics: study and application of electronic devices that source, detect and control light. Mechanical: a system that manages power to accomplish a task that involves forces and movement.

Optical elements application Micro-mirror Micro-mirror array Micro diffractive grating Micro waveguides Optical elements application

MOEMS Applications Micro-sensor for cell growth. -University of Illinois researchers

Con’t Micro optical scanner. Microsystem What is optical scanner? -University of Sttrathclyde researchers What is optical scanner? -A device that can read text or illustrations printed on paper and translate the information into a form the computer can use. - A scanner works by digitizing an image , dividing it into a grid of boxes and representing each box with either a zero or a one, depending on whether the box is filled in Microsystem

DMD by Texas Instrument -A DMD chip has on its surface several hundred thousand microscopic mirrors arranged in a rectangular array which correspond to the pixels in the image to be displayed. -The mirrors can be individually rotated ±10-12°, to an on or off state. -In the on state, light from the projector bulb is reflected into the lens making the pixel appear bright on the screen. In the off state, the light is directed elsewhere making the pixel appear dark

MEMS Nanosensor HI-MEMS (Hybrid Insect MEMS)

Micro-machining Micromachining Bulk micromachining Surface Refers to techniques for fabrication device structures on the micrometer scale. A portion of substrate (bulk) is removed in order to create freestanding mechanical structures (beams or membranes) or unique 3D features (gear, holes, cavities). MOEMS applications e.g.: Sensor: camera-on-a-chip, nose-on-chip, Data storage: magnetic data storage (use actuators). Displays: DMD (digital mirror devices)-metrology tools, TV, cinema. Military purposes: embedded sensors and actuators in weapon system. Primarily on Si substrate. Micromachining Bulk micromachining Surface micromachining

Bulk Micromachining Process for producing 3D MEMS structures – older process (sometime called etching). Involves the removal of silicon from the bulk silicon substrate by using a chemical liquid. Uses anisotropic and isotropic etching of single crystal silicon. Example: silicon cantilever beam for atomic force microscope.

Con’t Anisotropic etchants, etch different silicon orientation planes at different rates. Dopant diffusion Masking Anisotropic etching

Con’t Isotropic etchants, on the other hand, etch the silicon evenly in all directions.

Bulk Micromachining Etching process:

Bulk Micromachining Wet etch/liquid etch: The key ingredients are: Transport of reactants to the surface Surface reaction Transport of products from surfaces The key ingredients are: Buffered HF (BHF) to etch SiO2 Acid or base to dissolve the oxidized surface (e.g H2SO4, NH4OH) Dilutent media to transport the products through (e.g. H2O)

Bulk Micromachining Can be iso- and anisotropy. Anisotropy, use different etchant for different orientation. Example: KOH) displays an etch rate selectivity 400 times higher in <100> crystal directions than in <111> directions. Tetra-methyl-ammonium (TMAH) has 37X selectivity between {100} and {111} planes in silicon.

Bulk Micromachining Dry etch:

Bulk Micromachining Highly selective. RF excite ion/atoms. The plasma hits the silicon wafer with high energy and bombard the Si atoms on the surface. Typical plasma of reactive gases such as fluorocarbons, oxygen, chlorine, boron trichloride. Useful for chemically resistant such as silicon carbide or gallium nitride.

Bulk Micromachining Chemical dry etching (also called vapor phase etching) does not use liquid chemicals or etchants. Involves a chemical reaction between etchant gases to attack the silicon surface. The chemical dry etching process is usually isotropic and exhibits high selectively. Anisotropic Dry etching has the ability to etch with finer resolution and higher aspect ratio than isotropic etching. Some of the ions that are used in chemical dry etching is methane (CH4), sulfur hexafluoride (SF6), nitrogen trifluoride (NF3), chlorine gas (Cl2), or fluorine (F2).

Bulk Micromachining RIE: uses both physical and chemical mechanisms to achieve high levels of resolution. The high energy collision from the ionization helps to dissociate the etchant molecules into more reactive species. Cations are produced from reactive gases which are accelerated with high energy to the substrate and chemically react with the silicon. The typical RIE gasses for Si are CF4, SF6 and BCl2 + Cl2.

Surface Micromachining Unlike bulk micromachining where a silicon substrate (wafer) is selectively etched to produce structures, surface micromachining builds microstructures by deposition and etching of different structural layers on top of the substrate. Generally polysilicon is commonly used as one of the layers and silicon dioxide is used as a sacrificial layer which is removed or etched out to create the necessary void in the thickness direction. Added layers are generally very thin with their size varying from 2-5 Micro metres.

Surface Micromachining Typical components are structural layer and sacrificial layer. Material for structural layer is polycrystalline silicon while material for sacrificial layer is phosphosilicate glass (PSG). The surface micromachined components are smaller compared to their counterparts, the bulk micromachined

Ti (sacrificial layer) Silicon Substrate PMMA Ti Ni Deposit Ti as sacrificial layer Etch Ti X-Ray Lithography Strip PPMA Deposit Ni Etch Ti as sacrificial layer 1 2 3 4 5 6

LIGA LIGA: The abbreviation of three German words: + Lithographie (lithography in English) + Galvanoformung (electroplating) + Abformung (moulding). The primary advantage of LIGA process is its capability to make large aspect ratio structures (can be up to 1000 μm thick while only several micron wide).

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