MEMS- Micro ELectro Mechanical systems

ME407 MECHATRONICS SUKESH O P Assistant Professor Dept. of Mechanical Engineering JECC 10/16/2018 1 SUKESH O P/ APME/ME407- MR-2018

ME407 MECHATRONICS  Course Objectives:  To introduce the features of various sensors used in CNC machines and robots  To study the fabrication and functioning of MEMS pressure and inertial sensors  To enable development of hydraulic/pneumatic circuit and PLC programs for simple applications 10/16/2018 2 SUKESH O P/ APME/ME407- MR-2018

Expected outcome: The students will be able to i. Know the mechanical systems used in mechatronics ii. Integrate mechanical, electronics, control and computer engineering in the design of mechatronics systems ME407 MECHATRONICS 10/16/2018 3 SUKESH O P/ APME/ME407- MR-2018

Expected outcome: The students will be able to i. Know the mechanical systems used in mechatronics ii. Integrate mechanical, electronics, control and computer engineering in the design of mechatronics systems ME407 MECHATRONICS 10/16/2018 4 SUKESH O P/ APME/ME407- MR-2018

SYLLABUS  Introduction to Mechatronics, sensors, Actuators, Micro Electro Mechanical Systems (MEMS), Mechatronics in Computer Numerical Control (CNC) machines, Mechatronics in Robotics-Electrical drives, Force and tactile sensors, Image processing techniques, Case studies of Mechatronics systems. 10/16/2018 5 SUKESH O P/ APME/ME407- MR-2018

MODULE-III  Micro Electro Mechanical Systems (MEMS): Fabrication: Deposition, Lithography, Micromachining methods for MEMS, Deep Reactive Ion Etching (DRIE) and LIGA processes. Principle, fabrication and working of MEMS based pressure sensor, accelerometer and gyroscope 10/16/2018 6 SUKESH O P/ APME/ME407- MR-2018

MEMS  It is a technology that in its most general form can be defi ned as miniatured mechanical and electro-mechanical ele ments that are made using techniques of micromachining.  Made up of components between 1-100 micrometers in si ze (i.e., 0.001 to 0.1mm) and MEMS devices range in size from 20micrometers to millimeter(0.02 to 1.0mm)  Used for sensing, actuation or are passive micro-structures  Usually integrated with electronic circuitry for control and /or information processing 10/16/2018 7 SUKESH O P/ APME/ME407- MR-2018

Components of MEMS Microelectronics: “ brain ” that receives, processes, and makes decisions data comes from microsensors Microsensors: constantly gather data from environment pass data to microelectronics for processing can monitor mechanical, thermal, biological, chemical optical, and magnetic readings Microactuator: acts as trigger to activate external device microelectronics will tell microactuator to activate device Microstructures: extremely small structures built onto surface of chip built right into silicon of MEMS SUKESH O P/ APME/ME407- MR-2018

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Advantages of MEMS  Better stability and higher accuracy in the performance.  Miniaturization.  Integration of sensors and electronics on the same device.  Mass fabrication at low cost. 10/16/2018 10 SUKESH O P/ APME/ME407- MR-2018

Applications of MEMS 10/16/2018 11 SUKESH O P/ APME/ME407- MR-2018

Applications of MEMS 10/16/2018 12 SUKESH O P/ APME/ME407- MR-2018

Fabrication of MEMS  The basic techniques used in the fabrication of MEMS is deposition of one material over another material then, patterning using photolithography and then by etching the required shape. 10/16/2018 13 SUKESH O P/ APME/ME407- MR-2018

Fabrication of MEMS 10/16/2018 14 SUKESH O P/ APME/ME407- MR-2018

1. Deposition 10/16/2018 15 SUKESH O P/ APME/ME407- MR-2018

PVD  In PVD deposition technology, the material is removed from the source/ target and is deposited/transferred to the substrate. 10/16/2018 16 SUKESH O P/ APME/ME407- MR-2018

PVD  Physical vapor deposition ("PVD") consists of a process in which a material is removed from a target, and deposited on a surface.  Techniques to do this include the process of sputtering, in which an ion beam liberates atoms from a target, allowing them to move through the intervening space and deposit on the desired substrate, and evaporation, in which a material is evaporated from a target using either heat (thermal evaporation) or an electron beam (e-beam evaporation) in a vacuum system. 10/16/2018 17 SUKESH O P/ APME/ME407- MR-2018

CVD  Chemical vapor deposition (CVD) is a deposition method used to produce high quality, high-performance, solid materials, typically under vacuum. The process is often used in the semiconductor industry to produce thin films.  Chemical deposition techniques include chemical vapor deposition ("CVD"), in which a stream of source gas reacts on the substrate to grow the material desired.  This can be further divided into categories depending on the details of the technique, for example, LPCVD (Low Pressure chemical vapor deposition) and PECVD (Plasma-enhanced chemical vapor deposition). 10/16/2018 22 SUKESH O P/ APME/ME407- MR-2018

2. Patterning transfer of a pattern into a material after deposition in order to prepare for etching.( like printing on a paper). techniques include some type of lithography, photolithography is common LITHOGRAPHY  Lithography in the MEMS context is typically the transfer of a pattern to a photosensitive material by selective exposure to a radiation source such as light.  A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source.  If photosensitive material is selectively expose to radiation light (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed and the properties of the exposed and unexposed regions different.  This exposed region can then be removed or treated by providing a mask for the underlying substrate. 10/16/2018 26 SUKESH O P/ APME/ME407- MR-2018

LITHOGRAPHY  Lithography in the MEMS context is typically the transfer of a pattern to a photosensitive material by selective exposure to a radiation source such as light.  A photosensitive material is a material that experiences a change in its physical properties when exposed to a radiation source.  If photosensitive material is selectively expose to radiation light (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed and the properties of the exposed and unexposed regions different.  This exposed region can then be removed or treated by providing a mask for the underlying substrate. 10/16/2018 27 SUKESH O P/ APME/ME407- MR-2018

 In lithography for micromachining, the photosensitive material used is typically a photoresist (also called resist, other photosensitive polymers are also used).  When resist is exposed to a radiation source of a specific a wavelength, the chemical resistance of the resist to developer solution changes. If the resist is placed in a developer solution after selective exposure to a light source, it will etch away one of the two regions (exposed or unexposed).  If the exposed material is etched away by the developer and the unexposed region is resilient, the material is considered to be a positive resist. If the exposed material is resilient to the developer and the unexposed region is etched away, it is considered to be a negative resist. 10/16/2018 29 SUKESH O P/ APME/ME407- MR-2018

 Few lithography techniques are:  Ion beam lithography  Ion track technology  X-ray lithography 10/16/2018 39 SUKESH O P/ APME/ME407- MR-2018

3. Etching  Etching is a process which makes it possible to selectively remove the deposited films or parts of the substrate in order to prepare a desired patterns, shapes, features, or structures.  Etching is used in micro fabrication to chemically remove layers from the surface of a wafer during manufacturing. 10/16/2018 40 SUKESH O P/ APME/ME407- MR-2018

 Etching  Wet etching Isotropic Anisotropic  Dry etching Plasma etching Reaction ion etching 10/16/2018 41 SUKESH O P/ APME/ME407- MR-2018

Wet etching  Wet etching removes the material selectively through chemical reaction.  The material is immersed in a chemical solution, which reacts and subsequently dissolves the portion of the material, which is in contact with the solution.  Materials not covered by the masks are left undissolved.  Dipping substrate into chemical solution that selectively removes material.  Process provides good selectivity, etching rate of target material higher that mask material 10/16/2018 42 SUKESH O P/ APME/ME407- MR-2018

Wet etching process fall under three sub-activities.  Diffusion of the etchant to the surface for removal. The operation is carried out at room temp. or slightly above, but preferably below 50C.  Establishment of reaction b/w the etchant and the material being removed.  Diffusion of the reaction by products from the reacted surface.- cleaning  The dissolution of material due to chemical reaction may not be uniform in all directions. This characteristic of etching is called directionality. 10/16/2018 43 SUKESH O P/ APME/ME407- MR-2018

 Anisotropic materials, the etch rates are not same in all directions. Anisotropic etching is considerably a highly directional etching process with different directions.  The name isotropic material will dissolve uniformly in all directions. In isotropic etching materials are removed uniformly from all directions and it is independent of the plane of orientation of the crystal lattice. 10/16/2018 44 SUKESH O P/ APME/ME407- MR-2018

Dry etching  A dry etching doesnot utilize any liquid chemicals or etchants to remove materials.  This etching process is primarily used in surface micromachining process. The main adv of dry etching are that the process eliminates handling of dangerous acids and solvents, uses small amounts of chemicals.  In dry etching sputter the material using reactive ions or a vapor etchant.  Material sputtered or dissolved from substrate with plasma or gas variations 10/16/2018 45 SUKESH O P/ APME/ME407- MR-2018

Deep Reactive Ion Etching (DRIE)  In DRIE, the substrate is placed inside a reactor, and several gases are introduced.  Chemical part : A plasma is struck in the gas mixture which breaks the gas molecules into ions. The ions accelerate towards, and react with the surface of the material being etched, forming another gaseous material.  Physical part : if the ions have high enough energy, they can knock atoms out of the material to be etched without a chemical reaction.  Major techniques are :-  Cryogenic process  Bosch process 10/16/2018 46 SUKESH O P/ APME/ME407- MR-2018

Deep Reactive Ion Etching (DRIE)  Cryogenic process: low temperature slows down the chemical reaction that produces isotropic etching. How ever, ions continuous to bombard upward facing surface and etch them away. This process produces trenches with highly vertical side walls.  Bosch process : also known as pulse (or) time multiplexed etching. It oscillates repeatedly between two modes to achieve nearly vertical structure. 10/16/2018 47 SUKESH O P/ APME/ME407- MR-2018

 Relatively new technology.  Enables very high aspect ratio etches.  Uses high density plasma to alternately etch and deposit etch resistant polymer on sidewalls. 10/16/2018 48 Deep Reactive Ion Etching (DRIE) SUKESH O P/ APME/ME407- MR-2018

Micro Machining  Fabrication of products deals with making of machines, structures or process equipment by casting, forming, welding, machining & assembling.  Classified into: Macro & micro  Macro: fabrication of structures/parts/products that are measurable observable by naked eye( ≥ 1mm in size).  Micro: fabrication of miniature structures/parts/products that are not visible with naked eye(1 µm ≤ dimension ≤ 1000 µm in size).  Methods of Micro Fabrication: Material deposition & Material Removal 10/16/2018 49 SUKESH O P/ APME/ME407- MR-2018

Why Micro Machining?  Present day High-tech Industries, Design requirements are stringent.  Extraordinary Properties of Materials (High Strength, High heat Resistant, High hardness, Corrosion resistant etc).  Complex 3D Components (Turbine Blades)  Miniature Features (filters for food processing and textile industries having few tens of microns as hole diameter and thousands in number)  Nano level surface finish on Complex geometries (thousands of turbulated cooling holes in a turbine blade)  Making and finishing of micro fluidic channels (in electrically conducting & non conducting materials, say glass, quartz, &ceramics) 10/16/2018 50 SUKESH O P/ APME/ME407- MR-2018

Bulk Micromaching  Bulk and surface micromachining are processes used to create microstructures on microelectromechanical MEMS devices.  While both wet and dry etching techniques are available to both bulk and surface micromachining, bulk micromachining typically uses wet etching techniques while surface micromachining primarily uses dry etching techniques.  Bulk micromachining selectively etches the silicon substrate to create microstructures on MEMS devices. 10/16/2018 51 SUKESH O P/ APME/ME407- MR-2018

Bulk Micromachining Bulk micromachining involves the removal of part of the bulk substrate. It is a subtractive process that uses wet anisotropic etching or a dry etching method such as reactive ion etching (RIE), to create large pits, grooves and channels. Materials typically used for wet etching include silicon and quartz, while dry etching is typically used with silicon, metals, plastics and ceramics.

SUKESH O P/ APME/ME407- MR-2018 Bulk Micromachining- Advantages/Disadvantages  Can be done much faster  Can make high aspect ratio parts  Cheaper  Not easily integrated with microelectronics  Part complexity must be relatively simple  Part size is limited to being larger

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.  The main advantage of this machining process is the possibility of realizing monolithic microsystems in which the electronic and the mechanical components(functions) are built in on the same substrate 10/16/2018 54 SUKESH O P/ APME/ME407- MR-2018

Surface Micromachining 10/16/2018 55 SUKESH O P/ APME/ME407- MR-2018

 Newer than Bulk Micromachining  Uses single sided wafer processing  Involves use of sacrificial and structural layers  Provides more precise dimensional control  Involves use of sacrificial and structural layers SUKESH O P/ APME/ME407- MR-2018

Surface Micromachining- Applications  Used in manufacturing of flat panel television screen.  Used in production of thin solar cells.  Used in making bimetal cantilever used for monitoring mercury vapour, moisture, protein conformational changes in antigen antibody binding. 10/16/2018 57 SUKESH O P/ APME/ME407- MR-2018

Surface Micromachining Advantages/Disadvantages  Possible to integrate mechanical and electrical components on same substrate  Can create structures that Bulk Micromachining cannot  Cheaper glass or plastic substrates can be used  Mechanical properties of most thin-films are usually unknown and must be measured  Reproducibility of mechanical properties can be difficult  More expensive

HIGH-ASPECT-RATIO ICROMACHINING  High-aspect-ratio micromachining (HARM) is a process that involves micromachining as a tooling step followed by injection moulding or embossing and, if required, by electroforming to replicate microstructures in metal from moulded parts. It is one of the most attractive technologies for replicating microstructures at a high performance-to-cost ratio and includes techniques known as LIGA. 10/16/2018 60 SUKESH O P/ APME/ME407- MR-2018

LIGA Process  Developed in Germany in the early 1980s.  LIGA stands for the German words  LIthographie (in particular X-ray lithography)  Galvanoformung (translated electrodeposition or electroforming)  Abformtechnik (plastic molding) 10/16/2018 61 SUKESH O P/ APME/ME407- MR-2018

 Popular high aspect ratio micromachining technology  Primarily non-Silicon basted and requires use of x-ray radiation  Special mask and x-ray radiation makes process expensive 10/16/2018 64 SUKESH O P/ APME/ME407- MR-2018

Advantages of LIGA  LIGA is a versatile process – it can produce parts by several different methods  High aspect ratios are possible (large heightto-width ratios in the fabricated part)  Wide range of part sizes is feasible - heights ranging from micrometers to centimeters  Close tolerances are possible 10/16/2018 66 SUKESH O P/ APME/ME407- MR-2018

Disadvantages of LIGA  LIGA is a very expensive process  Large quantities of parts are usually required to justify its application  LIGA uses X-ray exposure  Human health hazard 10/16/2018 67 SUKESH O P/ APME/ME407- MR-2018

 Principle, fabrication and working of MEMS based pressure sensor, accelerometer and gyroscope 10/16/2018 72 SUKESH O P/ APME/ME407- MR-2018

10/16/2018 73 SUKESH O P/ APME/ME407- MR-2018 Sensors

MEMS-based accelerometer  MEMS-based accelerometer with capacitors is typically a structure that uses two capacitors formed by a moveable plate held between two fixed plates.  Under zero net force the two capacitors are equal but a change in force will cause the moveable plate to shift closer to one of the fixed plates, increasing the capacitance, and further away from the other fixed reducing that capacitance.  This difference in capacitance is detected and amplified to produce a voltage proportional to the acceleration 10/16/2018 79 SUKESH O P/ APME/ME407- MR-2018

Thank you End of module 3 10/16/2018 95 SUKESH O P/ APME/ME407- MR-2018

MEMS- Micro ELectro Mechanical systems

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