America's Next Bomber

America’s next bomber could cost $810 million apiece>>

The U.S. Air Force’s new long-range bomber may cost as much as $81 billion for the 100 planes planned, 47 percent more than the $55 billion sticker price the service has listed.
The Air Force based its estimate of $550 million per plane on the value of the dollar in 2010, and it represents only the production costs for an aircraft that won’t be deployed for at least 10 years. Including research and development, the bomber would cost as much as $810 million apiece in this year’s dollars, according to calculations by three defense analysts.
The cost of the new bomber will draw close scrutiny in an era of declining defense budgets, as the Pentagon faces $500 billion in reductions over nine years under the budget process called sequestration. The Air Force’s track record also is being questioned after soaring costs for the aging B-2 stealth bomber the new plane would replace and the F-35 fighter jet, the most expensive U.S. weapons system, that’s now being built.
“The Air Force has zero credibility on start-of-program cost estimates unless and until it ponies up real details about the bomber and its acquisition plan,” Winslow Wheeler, a former Government Accountability Office defense analyst now with the Project on Government Oversight in Washington, said in an e-mail. “It is a fool’s errand, or worse, to pretend the cost stated now is anything but a bait-and-switch buy-in gambit.”
B-2, F-35
The B-2 was planned as 132 planes for about $571 million each in 1991 dollars before the first Bush administration cut the fleet to 20 planes in the early 1990s. That resulted in a price of about $2.2 billion per bomber, a fourfold increase, in a program that remained highly classified during its development.
The F-35 program has a current price tag of $391.2 billion for 2,443 aircraft, a 68 percent increase from the projection in 2001, as measured in current dollars, for 409 fewer planes than originally planned.
Whatever its ultimate cost, the new bomber would mean billions for the defense contractor chosen to build it. Lockheed Martin Corp. (LMT:US) of Bethesda, Maryland, and Chicago-based Boeing Co. (BA:US), the No. 1 and No. 2 U.S. defense contractors, said in October that they’ll bid for the project as a team. They may end up competing against Northrop Grumman Corp. (NOC:US) of Falls Church, Virginia, the prime contractor for the B-2, which hasn’t yet announced an intention to bid.
The Air Force has requested $379 million in funding for development this year, increasing to more than $1 billion in fiscal 2015 and $2.8 billion in fiscal 2018, according to data released by the service.
Through 2023
The Air Force hasn’t provided its rationale for the increased spending. The Congressional Budget Office said the Air Force plans to request $32.1 billion through 2023.
The $550 million per plane projection for the new bomber is “the only cost estimate approved for public release at this time,” Air Force spokesman Ed Gulick said in a statement.
Gulick said the estimate is a “target that helps balance capabilities and cost” and is being used in “rigidly containing the design” of the bomber.
The more complete “program acquisition unit cost” will be derived later by adding research and development, as well as estimating “inflation up to the year you purchase aircraft,” Gulick said.
The Air Force’s cost estimate “seems rather ambitious,” said Todd Harrison, a defense budget analyst with the Center for Strategic and Budgetary Assessments, a Washington-based policy group. He calculated a price of $810 million a plane in fiscal 2014 dollars, or $81 billion for 100, based on $20 billion in projected research and development costs.
Historical Increases
“Aircraft programs, and stealth aircraft in particular, have gone far over their initial cost estimates,” Harrison said. “If you factor in historical cost growth, the total program cost could easily top $100 billion.”
Russell Rumbaugh, a defense analyst with the Stimson Center, also a policy group in Washington, said his comparable estimate is $682 million per plane. Kevin Brancato, a defense analyst with Bloomberg Government, projected $784 million per plane in this year’s dollars.
“The incentives in the budget system almost force the services to low-ball their cost estimates,” said Gordon Adams, a professor at American University in Washington who oversaw the national security budget for the White House under President Bill Clinton. “Otherwise they do not get the program in the budget. It grows later.”
The Air Force now operates a fleet of 159 long-range bombers, including 63 swing-wing B-1Bs developed in the 1980s by Rockwell International, which is now part of Boeing, and the 20 B-2s from the 1990s.
Aging B-2s
The new bomber is needed because the “B-2 is an older airplane that’s getting expensive” to maintain and “it’s not as stealthy as we’re now capable of making aircraft,” Deputy Defense Secretary Ashton Carter said in an interview before he left office Dec. 4.
As the Air Force anticipates its needs 10 or 20 years from now, “expecting those aircraft to perform reliably at such advanced ages may prove to be overly optimistic,” said Mark Gunzinger, an airpower analyst with the Center for Strategic and Budgetary Assessments.
The Air Force is still flying 76 B-52 bombers from the H series that entered service in May 1961. They remain capable of launching conventional and nuclear bombs and cruise missiles.
Top Projects
The Air Force has identified the new long-range bomber as one of its top three weapons projects, along with the F-35 from Lockheed and the KC-46 aerial refueling tanker made by Boeing.
Defense Secretary Chuck Hagel has said the bomber will support the U.S. strategy of rebalancing toward Asia. Pentagon officials have said they’ll do as much as they can to shelter such priority weapons systems from the automatic budget cuts.
An Air Force summary of the bomber describes a stealth aircraft able to deliver both nuclear and conventional weapons. While the “baseline aircraft” would be piloted, the bomber would be designed to “enable future unmanned capability,” according to the service.
Beyond that, the Air Force, which has said the bomber would incorporate “proven technologies,” has said little about its classified plans for the new plane.
“It would be a mistake to view this aircraft as simply another bomber,” said Retired Lieutenant General David Deptula, the Air Force’s former chief of intelligence, surveillance and reconnaissance.
‘Cloaked in Secrecy’
It may take off on a bombing run, using intelligence and surveillance sensors provided from other platforms and on-board jammers to degrade ground radar, he said in an e-mail. The bomber crew also could use its radar and sensors to direct land-and sea-based strikes, as well as collect intelligence on the return flight, according to Deptula, who helped plan the air campaign in the 1991 Gulf War.
“The operational characteristics are going to be cloaked in secrecy for a while, and I think that makes perfect sense,” Air Force Chief of Staff General Mark Welsh told reporters in November.
Welsh said capabilities would be carefully weighed against the $550 million-a-plane target.
“What we don’t want to do is try to reach into some level of technology that’s impractical.” That’s when “prices start to get out of control and your requirements start to drift,” Welsh said. “We are not going to go there.”
Adams cited the B-2’s cost escalation, as well as plans for a medium-range bomber that Defense Secretary Robert Gates canceled as too costly in 2009. Gates supports the new bomber.
“How many times are we going to go down this overpriced bomber road?” said Adams said. “It’s like Lucy with the football. We never get to kick an affordable aircraft through the goalpost.”

Arduino 4d9a3348ad10c407354911e17196ac65c564a40

Arduino is a single-board microcontroller to make using electronics in multidisciplinary projects more accessible. The hardware consists of an open-source hardware board designed around an 8-bit Atmel AVR microcontroller, or a 32-bit Atmel ARM. The software consists of a standard programming language compiler and a boot loader that executes on the microcontroller.

Arduino boards can be purchased pre-assembled or as do-it-yourself kits. Hardware design information is available for those who would like to assemble an Arduino by hand. It was estimated in mid-2011 that over 300,000 official Arduinos had been commercially produced.

An arduino board consists of an Atmel 8-bit AVR microcontroller with complementary components to facilitate programming and incorporation into other circuits. An important aspect of the Arduino is the standard way that connectors are exposed, allowing the CPU board to be connected to a variety of interchangeable add-on modules known as shields. Some shields communicate with the Arduino board directly over various pins, but many shields are individually addressable via an I²C serial bus, allowing many shields to be stacked and used in parallel. Official Arduinos have used the megaAVR series of chips, specifically the ATmega8, ATmega168, ATmega328, ATmega1280, and ATmega2560. A handful of other processors have been used by Arduino compatibles. Most boards include a 5 voltlinear regulator and a 16 MHz crystal oscillator (or ceramic resonator in some variants), although some designs such as the LilyPad run at 8 MHz and dispense with the onboard voltage regulator due to specific form-factor restrictions. An Arduino's microcontroller is also pre-programmed with a boot loader that simplifies uploading of programs to the on-chip flash memory, compared with other devices that typically need an external programmer.

At a conceptual level, when using the Arduino software stack, all boards are programmed over an RS-232 serial connection, but the way this is implemented varies by hardware version. Serial Arduino boards contain a level shifter circuit to convert between RS-232-level andTTL-level signals. Current Arduino boards are programmed via USB, implemented using USB-to-serial adapter chips such as the FTDIFT232. Some variants, such as the Arduino Mini and the unofficial Boarduino, use a detachable USB-to-serial adapter board or cable,Bluetooth or other methods. (When used with traditional microcontroller tools instead of the Arduino IDE, standard AVR ISPprogramming is used.)

The Arduino board exposes most of the microcontroller's I/O pins for use by other circuits. The Diecimila, Duemilanove, and current Uno provide 14 digital I/O pins, six of which can produce pulse-width modulated signals, and six analog inputs. These pins are on the top of the board, via female 0.10-inch (2.5 mm) headers. Several plug-in application shields are also commercially available.

The Arduino Nano, and Arduino-compatible Bare Bones Board and Boarduino boards may provide male header pins on the underside of the board to be plugged into solderless breadboards.

There are many Arduino-compatible and Arduino-derived boards. Some are functionally equivalent to an Arduino and may be used interchangeably. Many are the basic Arduino with the addition of commonplace output drivers, often for use in school-level education to simplify the construction of buggies and small robots. Others are electrically equivalent but change the form factor, sometimes permitting the continued use of Shields, sometimes not. Some variants use completely different processors, with varying levels of compatibility.

Official boards

Further information: List of Arduino boards and compatible systems

The original Arduino hardware is manufactured by the Italian company Smart Projects.Some Arduino-branded boards have been designed by the American company SparkFun Electronics.Sixteen versions of the Arduino hardware have been commercially produced to date.

• Example Arduino boards
• 

  Arduino Diecimila
 
• 

  Arduino Duemilanove (rev 2009b)
 
• 

  Arduino UNO
 
• 

  Arduino Leonardo
 
• 

  Arduino Mega
 
• 

  Arduino Nano
 
• 

  Arduino Due (ARM-based)
 
• 

  LilyPad Arduino (rev 2007)

Shields

Arduino and Arduino-compatible boards make use of shields—printed circuit expansion boards that plug into the normally supplied Arduino pin-headers. Shields can provide motor controls, GPS, ethernet, LCD display, or breadboarding (prototyping). A number of shields can also be made.

Example Arduino shields

• 

  Multiple shields can be stacked. In this example the top shield contains a solderless breadboard
 
• 

  Screw-terminal breakout shield in a wing-type format
 
• 

  Adafruit Motor Shield with screw terminals for connection to motors
 
• 

  Adafruit Datalogging Shield with a SD slot and Real-Time Clock chip

Software

Arduino Software IDE

A screenshot of the Arduino IDE showing the "Blink" program, a simple beginner program
Developer(s)	Arduino Software
Stable release	1.0.5 / May 15, 2013[9]
Preview release	1.5.4 Beta / September 10, 2013
Written in	Java, C and C++
Operating system	Cross-platform
Type	Integrated development environment
License	LGPL or GPL license
Website	arduino.cc

The Arduino integrated development environment (IDE) is a cross-platform application written in Java, and is derived from the IDE for theProcessing programming language and the Wiring projects. It is designed to introduce programming to artists and other newcomers unfamiliar with software development. It includes a code editor with features such as syntax highlighting, brace matching, and automatic indentation, and is also capable of compiling and uploading programs to the board with a single click. A program or code written for Arduino is called a "sketch".^[10]

Arduino programs are written in C or C++. The Arduino IDE comes with a software library called "Wiring" from the original Wiring project, which makes many common input/output operations much easier. Users only need define two functions to make a runnablecyclic executive program:

• setup(): a function run once at the start of a program that can initialize settings
• loop(): a function called repeatedly until the board powers off

A typical first program for a microcontroller simply blinks an LED on and off. In the Arduino environment, the user might write a program like this:^[11]

The integrated pin 13 LED

#define LED_PIN 13
 
void setup () {
  pinMode (LED_PIN, OUTPUT); // Enable pin 13 for digital output
}
 
void loop () {
  digitalWrite (LED_PIN, HIGH); // Turn on the LED
  delay (1000); // Wait one second (1000 milliseconds)
  digitalWrite (LED_PIN, LOW); // Turn off the LED
  delay (1000); // Wait one second
}

It is a feature of most Arduino boards that they have an LED and load resistor connected between pin 13 and ground; a convenient feature for many simple tests. The previous code would not be seen by a standard C++ compiler as a valid program, so when the user clicks the "Upload to I/O board" button in the IDE, a copy of the code is written to a temporary file with an extra include header at the top and a very simple main() function at the bottom, to make it a valid C++ program.

The Arduino IDE uses the GNU toolchain and AVR Libc to compile programs, and uses avrdude to upload programs to the board.

As the Arduino platform uses Atmel microcontrollers, Atmel's development environment, AVR Studio or the newer Atmel Studio, may also be used to develop software for the Arduino.

Development

The core Arduino developer team is composed of Massimo Banzi, David Cuartielles, Tom Igoe, Gianluca Martino, David Mellis and Nicholas Zambetti. Massimo Banzi was interviewed on the March 21st, 2009 episode (Episode 61) of FLOSS Weekly on the TWiT.tvnetwork, in which he discussed the history and goals of the Arduino project. He also gave a talk at TEDGlobal 2012 Conference, where he outlined various uses of Arduino boards around the world.Arduino is open source hardware: the Arduino hardware reference designs are distributed under a Creative Commons Attribution Share-Alike 2.5 license and are available on the Arduino Web site. Layout and production files for some versions of the Arduino hardware are also available. The source code for the IDE is available and released under the GNU General Public License, version 2.Although the hardware and software designs are freely available under copyleft licenses, the developers have requested that the name "Arduino" be exclusive to the official productand not be used for derivative works without permission. The official policy document on the use of the Arduino name emphasizes that the project is open to incorporating work by others into the official product.[Several Arduino-compatible products commercially released have avoided the "Arduino" name by using "-duino" name variants

Applications

Xoscillo: open-source oscilloscope
Scientific equipment
Arduinome: a MIDI controller device that mimics the Monome
OBDuino: a trip computer that uses the on-board diagnostics interface found in most modern cars
The Humane Reader and Humane PC from Humane Informatics: low-cost electronic devices with TV-out that can hold a five thousand book library (e.g. offline Wikipedia compilations) on a microSD card
Ardupilot: drone software / hardware
ArduinoPhone

Microelectromechanical systems

Microelectromechanical systems (MEMS) (also written as micro-electro-mechanical, MicroElectroMechanical or microelectronic and microelectromechanical systems) is the technology of very small devices; it merges at the nano-scale into nanoelectromechanical systems (NEMS) and nanotechnology. MEMS are also referred to as micromachines (in Japan), or micro systems technology – MST (in Europe).

MEMS are separate and distinct from the hypothetical vision of molecular nanotechnology or molecular electronics. MEMS are made up of components between 1 to 100 micrometres in size (i.e. 0.001 to 0.1 mm), and MEMS devices generally range in size from 20 micrometres (20 millionths of a metre) to a millimetre (i.e. 0.02 to 1.0 mm). They usually consist of a central unit that processes data (the microprocessor) and several components that interact with the surroundings such as microsensors.At these size scales, the standard constructs of classical physics are not always useful. Because of the large surface area to volume ratio of MEMS, surface effects such as electrostatics and wetting dominate over volume effects such as inertia or thermal mass.

The potential of very small machines was appreciated before the technology existed that could make them—see, for example, Richard Feynman's famous 1959 lecture There's Plenty of Room at the Bottom. MEMS became practical once they could be fabricated using modified semiconductor device fabrication technologies, normally used to make electronics. These include molding and plating, wet etching (KOH, TMAH) and dry etching (RIE and DRIE), electro discharge machining (EDM), and other technologies capable of manufacturing small devices. An early example of a MEMS device is the resonistor – an electromechanical monolithic resonator.

Materials for MEMS manufacturing

The fabrication of MEMS evolved from the process technology in semiconductor device fabrication, i.e. the basic techniques are deposition of material layers, patterning by photolithography and etching to produce the required shapes.

Silicon

Silicon is the material used to create most integrated circuits used in consumer electronics in the modern industry. The economies of scale, ready availability of cheap high-quality materials and ability to incorporate electronic functionality make silicon attractive for a wide variety of MEMS applications. Silicon also has significant advantages engendered through its material properties. In single crystal form, silicon is an almost perfect Hookean material, meaning that when it is flexed there is virtually no hysteresis and hence almost no energy dissipation. As well as making for highly repeatable motion, this also makes silicon very reliable as it suffers very little fatigue and can have service lifetimes in the range of billions to trillions of cycles without breaking.

Polymers

Even though the electronics industry provides an economy of scale for the silicon industry, crystalline silicon is still a complex and relatively expensive material to be produced. Polymers on the other hand can be produced in huge volumes, with a great variety of material characteristics. MEMS devices can be made from polymers by processes such as injection molding, embossing or stereolithography and are especially well suited to microfluidic applications such as disposable blood testing cartridges.

Metals

Metals can also be used to create MEMS elements. While metals do not have some of the advantages displayed by silicon in terms of mechanical properties, when used within their limitations, metals can exhibit very high degrees of reliability. Metals can be deposited by electroplating, evaporation, and sputtering processes. Commonly used metals include gold, nickel, aluminium, copper, chromium, titanium, tungsten, platinum, and silver.

Ceramics

The nitrides of silicon, aluminium and titanium as well as silicon carbide and other ceramics are increasingly applied in MEMS fabrication due to advantageous combinations of material properties. AlN crystallizes in the wurtzite structure and thus shows pyroelectric and piezoelectric properties enabling sensors, for instance, with sensitivity to normal and shear forces. TiN, on the other hand, exhibits a high electrical conductivity and large elastic modulus allowing to realize electrostatic MEMS actuation schemes with ultrathin membranes.Moreover, the high resistance of TiN against biocorrosion qualifies the material for applications in biogenic environments and in biosensors.

MEMS basic processes

Deposition processes

One of the basic building blocks in MEMS processing is the ability to deposit thin films of material with a thickness anywhere between a few nanometres to about 100 micrometres. There are two types of deposition processes, as follows.

Physical deposition

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 (deposition), 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.

Chemical deposition

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).

Oxide films can also be grown by the technique of thermal oxidation, in which the (typically silicon) wafer is exposed to oxygen and/or steam, to grow a thin surface layer of silicon dioxide.

Patterning

Patterning in MEMS is the transfer of a pattern into a material.

Lithography

Lithography in MEMS context is typically the transfer of a pattern into 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 a photosensitive material is selectively exposed to radiation (e.g. by masking some of the radiation) the pattern of the radiation on the material is transferred to the material exposed, as the properties of the exposed and unexposed regions differs.

This exposed region can then be removed or treated providing a mask for the underlying substrate. Photolithography is typically used with metal or other thin film deposition, wet and dry etching.

Photolithography

Photolithography is the process of transferring geometric shapes on a mask to the surface of a silicon wafer. The steps involved in the photolithographic process are wafer cleaning; barrier layer formation; photoresist application; soft baking; mask alignment; exposure and development; and hard-baking.

Wafer Cleaning, Barrier Formation and Photoresist Application

In the first step, the wafers are chemically cleaned to remove particulate matter on the surface as well as any traces of organic, ionic, and metallic impurities. After cleaning, silicon dioxide, which serves as a barrier layer, is deposited on the surface of the wafer. After the formation of the SiO2 layer, photoresist is applied to the surface of the wafer. High-speed centrifugal whirling of silicon wafers is the standard method for applying photoresist coatings in IC manufacturing. This technique, known as "Spin Coating," produces a thin uniform layer of photoresist on the wafer surface.

Positive and Negative Photoresist:-

There are two types of photoresist: positive and negative. For positive resists, the resist is exposed with UV light wherever the underlying material is to be removed. In these resists, exposure to the UV light changes the chemical structure of the resist so that it becomes more soluble in the developer. The exposed resist is then washed away by the developer solution, leaving windows of the bare underlying material. In other words, "whatever shows, goes." The mask, therefore, contains an exact copy of the pattern which is to remain on the wafer.

Negative resists behave in just the opposite manner. Exposure to the UV light causes the negative resist to become polymerized, and more difficult to dissolve. Therefore, the negative resist remains on the surface wherever it is exposed, and the developer solution removes only the unexposed portions. Masks used for negative photoresists, therefore, contain the inverse (or photographic "negative") of the pattern to be transferred. The figure below shows the pattern differences generated from the use of positive and negative resist.

Electron beam lithography

Electron beam lithography (often abbreviated as e-beam lithography) is the practice of scanning a beam of electrons in a patterned fashion across a surface covered with a film (called the resist),[7] ("exposing" the resist) and of selectively removing either exposed or non-exposed regions of the resist ("developing"). The purpose, as with photolithography, is to create very small structures in the resist that can subsequently be transferred to the substrate material, often by etching. It was developed for manufacturing integrated circuits, and is also used for creating nanotechnology architectures.

The primary advantage of electron beam lithography is that it is one of the ways to beat the diffraction limit of light and make features in the nanometer regime. This form of maskless lithography has found wide usage in photomask-making used in photolithography, low-volume production of semiconductor components, and research & development.

The key limitation of electron beam lithography is throughput, i.e., the very long time it takes to expose an entire silicon wafer or glass substrate. A long exposure time leaves the user vulnerable to beam drift or instability which may occur during the exposure. Also, the turn-around time for reworking or re-design is lengthened unnecessarily if the pattern is not being changed the second time.

Ion beam lithography

It is known that focused-ion-beam lithography has the capability of writing extremely fine lines (less than 50 nm line and space has been achieved) without proximity effect. However, because the writing field in ion-beam lithography is quite small, large area patterns must be created by stitching together the small fields.

Ion track technology

Ion track technology is a deep cutting tool with a resolution limit around 8 nm applicable to radiation resistant minerals, glasses and polymers. It is capable to generate holes in thin films without any development process. Structural depth can be defined either by ion range or by material thickness. Aspect ratios up to several 104 can be reached. The technique can shape and texture materials at a defined inclination angle. Random pattern, single-ion track structures and aimed pattern consisting of individual single tracks can be generated.

X-ray lithography

X-ray lithography, is a process used in electronic industry to selectively remove parts of a thin film. It uses X-rays to transfer a geometric pattern from a mask to a light-sensitive chemical photoresist, or simply "resist," on the substrate. A series of chemical treatments then engraves the produced pattern into the material underneath the photoresist.

Diamond patterning

Wiki letter w.svg This section is empty. You can help by adding to it. (January 2011)

Etching processes

There are two basic categories of etching processes: wet etching and dry etching. In the former, the material is dissolved when immersed in a chemical solution. In the latter, the material is sputtered or dissolved using reactive ions or a vapor phase etchant for a somewhat dated overview of MEMS etching technologies.

 Etching (microfabrication)

Wet chemical etching consists in selective removal of material by dipping a substrate into a solution that dissolves it. The chemical nature of this etching process provides a good selectivity, which means the etching rate of the target material is considerably higher than the mask material if selected carefully.

Isotropic etching

Etching progresses at the same speed in all directions. Long and narrow holes in a mask will produce v-shaped grooves in the silicon. The surface of these grooves can be atomically smooth if the etch is carried out correctly, with dimensions and angles being extremely accurate.

Anisotropic etching

Some single crystal materials, such as silicon, will have different etching rates depending on the crystallographic orientation of the substrate. This is known as anisotropic etching and one of the most common examples is the etching of silicon in KOH (potassium hydroxide), where Si <111> planes etch approximately 100 times slower than other planes (crystallographic orientations). Therefore, etching a rectangular hole in a (100)-Si wafer results in a pyramid shaped etch pit with 54.7° walls, instead of a hole with curved sidewalls as with isotropic etching.

HF etching

Hydrofluoric acid is commonly used as an aqueous etchant for silicon dioxide (SiO

2, also known as BOX for SOI), usually in 49% concentrated form, 5:1, 10:1 or 20:1 BOE (buffered oxide etchant) or BHF (Buffered HF). They were first used in medieval times for glass etching. It was used in IC fabrication for patterning the gate oxide until the process step was replaced by RIE.

Hydrofluoric acid is considered one of the more dangerous acids in the cleanroom. It penetrates the skin upon contact and it diffuses straight to the bone. Therefore the damage is not felt until it is too late.

Electrochemical etching

Electrochemical etching (ECE) for dopant-selective removal of silicon is a common method to automate and to selectively control etching. An active p-n diode junction is required, and either type of dopant can be the etch-resistant ("etch-stop") material. Boron is the most common etch-stop dopant. In combination with wet anisotropic etching as described above, ECE has been used successfully for controlling silicon diaphragm thickness in commercial piezoresistive silicon pressure sensors. Selectively doped regions can be created either by implantation, diffusion, or epitaxial deposition of silicon.

Xenon difluoride etching

Xenon difluoride is a dry vapor phase isotropic etch for silicon originally applied for MEMS in 1995 at University of California, Los Angeles.Primarily used for releasing metal and dielectric structures by undercutting silicon, XeF

2 has the advantage of a stiction-free release unlike wet etchants. Its etch selectivity to silicon is very high, allowing it to work with photoresist, SiO

2, silicon nitride, and various metals for masking. Its reaction to silicon is "plasmaless", is purely chemical and spontaneous and is often operated in pulsed mode. Models of the etching action are available, and university laboratories and various commercial tools offer solutions using this approach.

Reactive ion etching

In reactive ion etching (RIE), the substrate is placed inside a reactor, and several gases are introduced. A plasma is struck in the gas mixture using an RF power source, 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. This is known as the chemical part of reactive ion etching. There is also a physical part, which is similar to the sputtering deposition process. If the ions have high enough energy, they can knock atoms out of the material to be etched without a chemical reaction. It is a very complex task to develop dry etch processes that balance chemical and physical etching, since there are many parameters to adjust. By changing the balance it is possible to influence the anisotropy of the etching, since the chemical part is isotropic and the physical part highly anisotropic the combination can form sidewalls that have shapes from rounded to vertical. RIE can be deep (Deep RIE or deep reactive ion etching (DRIE)).

Deep reactive ion etching

Deep RIE (DRIE) is a special subclass of RIE that is growing in popularity. In this process, etch depths of hundreds of micrometres are achieved with almost vertical sidewalls. The primary technology is based on the so-called "Bosch process",[13] named after the German company Robert Bosch, which filed the original patent, where two different gas compositions alternate in the reactor. Currently there are two variations of the DRIE. The first variation consists of three distinct steps (the Bosch Process as used in the Plasma-Therm tool) while the second variation only consists of two steps (ASE used in the STS tool).

In the 1st Variation, the etch cycle is as follows:

(i) SF

6 isotropic etch;

(ii) C

4F

8 passivation;

(iii) SF

6 anisoptropic etch for floor cleaning.

In the 2nd variation, steps (i) and (iii) are combined.

Both variations operate similarly. The C

4F

8 creates a polymer on the surface of the substrate, and the second gas composition (SF

6 and O

2) etches the substrate. The polymer is immediately sputtered away by the physical part of the etching, but only on the horizontal surfaces and not the sidewalls. Since the polymer only dissolves very slowly in the chemical part of the etching, it builds up on the sidewalls and protects them from etching. As a result, etching aspect ratios of 50 to 1 can be achieved. The process can easily be used to etch completely through a silicon substrate, and etch rates are 3–6 times higher than wet etching.

Die preparation

After preparing a large number of MEMS devices on a silicon wafer, individual dies have to be separated, which is called die preparation in semiconductor technology. For some applications, the separation is preceded by wafer backgrinding in order to reduce the wafer thickness. Wafer dicing may then be performed either by sawing using a cooling liquid or a dry laser process called stealth dicing.

MEMS manufacturing technologies

Bulk micromachining

Bulk micromachining is the oldest paradigm of silicon based MEMS. The whole thickness of a silicon wafer is used for building the micro-mechanical structures.[9] Silicon is machined using various etching processes. Anodic bonding of glass plates or additional silicon wafers is used for adding features in the third dimension and for hermetic encapsulation. Bulk micromachining has been essential in enabling high performance pressure sensors and accelerometers that changed the sensor industry in the 1980's and 90's.

Surface micromachining

Surface micromachining uses layers deposited on the surface of a substrate as the structural materials, rather than using the substrate itself.Surface micromachining was created in the late 1980s to render micromachining of silicon more compatible with planar integrated circuit technology, with the goal of combining MEMS and integrated circuits on the same silicon wafer. The original surface micromachining concept was based on thin polycrystalline silicon layers patterned as movable mechanical structures and released by sacrificial etching of the underlying oxide layer. Interdigital comb electrodes were used to produce in-plane forces and to detect in-plane movement capacitively. This MEMS paradigm has enabled the manufacturing of low cost accelerometers for e.g. automotive air-bag systems and other applications where low performance and/or high g-ranges are sufficient. Analog Devices have pioneered the industrialization of surface micromachining and have realized the co-integration of MEMS and integrated circuits.

High aspect ratio (HAR) silicon micromachining

Both bulk and surface silicon micromachining are used in the industrial production of sensors, ink-jet nozzles, and other devices. But in many cases the distinction between these two has diminished. A new etching technology, deep reactive-ion etching, has made it possible to combine good performance typical of bulk micromachining with comb structures and in-plane operation typical of surface micromachining. While it is common in surface micromachining to have structural layer thickness in the range of 2 µm, in HAR silicon micromachining the thickness can be from 10 to 100 µm. The materials commonly used in HAR silicon micromachining are thick polycrystalline silicon, known as epi-poly, and bonded silicon-on-insulator (SOI) wafers although processes for bulk silicon wafer also have been created (SCREAM). Bonding a second wafer by glass frit bonding, anodic bonding or alloy bonding is used to protect the MEMS structures. Integrated circuits are typically not combined with HAR silicon micromachining.

Applications

microelectromechanical systems chip, sometimes called "lab on a chip"

MEMS compared to a 0.02 € coin

In one viewpoint MEMS application is categorized by type of use.

Sensor

Actuator

Structure

In another view point MEMS applications are categorized by the field of application (commercial applications include):

Inkjet printers, which use piezoelectrics or thermal bubble ejection to deposit ink on paper.

Accelerometers in modern cars for a large number of purposes including airbag deployment in collisions.

Accelerometers in consumer electronics devices such as game controllers (Nintendo Wii), personal media players / cell phones (Apple iPhone, various Nokia mobile phone models, various HTC PDA models)[15] and a number of Digital Cameras (various Canon Digital IXUS models). Also used in PCs to park the hard disk head when free-fall is detected, to prevent damage and data loss.

MEMS gyroscopes used in modern cars and other applications to detect yaw; e.g., to deploy a roll over bar or trigger dynamic stability control

MEMS microphones in portable devices, e.g., mobile phones, head sets and laptops.

Silicon pressure sensors e.g., car tire pressure sensors, and disposable blood pressure sensors

Displays e.g., the DMD chip in a projector based on DLP technology, which has a surface with several hundred thousand micromirrors or single micro-scanning-mirrors also called microscanners

Optical switching technology, which is used for switching technology and alignment for data communications

Bio-MEMS applications in medical and health related technologies from Lab-On-Chip to MicroTotalAnalysis (biosensor, chemosensor), or embedded in medical devices e.g. stents.

Interferometric modulator display (IMOD) applications in consumer electronics (primarily displays for mobile devices), used to create interferometric modulation − reflective display technology as found in mirasol displays

Fluid acceleration such as for micro-cooling

Micro-scale Energy harvesting including piezoelectric,electrostatic and electromagentic micro harvesters.

Micromachined Ultrasound Transducer including Piezoelectric Micromachined Ultrasonic Transducers and Capacitive Micromachined Ultrasonic Transducers.

Companies with strong MEMS programs come in many sizes. The larger firms specialize in manufacturing high volume inexpensive components or packaged solutions for end markets such as automobiles, biomedical, and electronics. The successful small firms provide value in innovative solutions and absorb the expense of custom fabrication with high sales margins. In addition, both large and small companies work in R&D to explore MEMS technology.

Industry structure

The global market for micro-electromechanical systems, which includes products such as automobile airbag systems, display systems and inkjet cartridges totaled $40 billion in 2006 according to Global MEMS/Microsystems Markets and Opportunities, a research report from SEMI and Yole Developpement and is forecasted to reach $72 billion by 2011.

MEMS devices are defined as die-level components of first-level packaging, and include pressure sensors, accelerometers, gyroscopes, microphones, digital mirror displays, microfluidic devices, etc. The materials and equipment used to manufacture MEMS devices topped $1 billion worldwide in 2006. Materials demand is driven by substrates, making up over 70 percent of the market, packaging coatings and increasing use of chemical mechanical planarization (CMP). While MEMS manufacturing continues to be dominated by used semiconductor equipment, there is a migration to 200 mm lines and select new tools, including etch and bonding for certain MEMS applications.