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Using MEMS to Miniaturize Mobile Phones
securitas writes: "The NY Times has a feature on using microelectro-mechanical systems (MEMS) in cell phones to replace bulky passive components like the filters, resonators and duplexers that make up most of the size of today's phones. In theory, they say, you could have a cell phone in a ring on your finger. Besides making everyone seem like James Bond, a ring-phone would give new meaning to the phrase 'Talk to the hand.'"
I am working in the MEMs area these days. So here are some shameless plugs.
...)
Here
is an general interest article from the group in which I work with some details oriented towards these types of mesoscopic MEMs.
Here
is a neat picture of a Mesoscopic MEMs device (an acceleratometer resting on top the middle part of the "8" in a 1998 penny.
And though my research at Berkeley wasn't MEMS oriented, Berkeley MEMS is pretty active. Here is a link to that.
As the article points out, MEMS are finding applications in cell phones because it is easy to make very small RF filters using inertial effects to provide inductive-like impedences. (In the past, the inductive like parts of a cell-phone filter would either be done with spiral inductors, which are unwieldly or via other microwave circuit voodoo.)
However, beyond cell phones is a grab bag of MEMs applications already at or beyond the prototype stage:
- Car air bag detectors (the above accelerometer)
- Laser gyroscopes
- Projection displays (pixel mirrors arrays)
- Optical fiber switches
- Medical applications (microfluidics, bio-chips,
- Remote sensing (minaturized microphones, or in the future, smart dust)
Enjoy
Kevin
. . . to reduce the size of the phone will reduce the size of the battery . . .
"Luckily," he says dryly, "the article answers this very issue."
Indirectly, better filtering helps reduce the size of a cellphone because lower-quality filtering results in a signal loss that is corrected by more amplification, which drains power. More power means bigger batteries and extra electronics within the phone.
"The ultimate benefit," Mr. Mueller said, "is a smaller, lighter phone that works well and works longer between charges."
The Gardener
--
For people like me who had no idea what coltan is, see this article. The short version is that columbite-tantalite (coltan) is an ore than can be refined into tantalum, which apparently is a very good dielectric for making capacitors. This means that it's not just in cell phones but probably in every electronic device you own.
The controversy over coltan and the Congo seems to revolve around two issues. One is that Congo's neighbors seem to be exploiting its coltan resources, i.e. smuggling coltan and exporting it as their own product. Another is the environmental impact, since illegal mining operations probably care as much about the environmental impact they have as they do about the law.
All of this so far is off-topic, but if rf MEMs could replace capacitive filters and resonators, it could help reduce the demand for coltan. This feeble attempt to be on-topic is purely speculative, though, as I am not a wireless engineer and the NYT article lacks details about the materials being used in these devices.
"It take 9 months to bear a child, no matter how many women you assign to the job."
What is Coltan
Coltan killing elephants, gorillas and people
The Coltan Rush
Minerals Fueling War
Guns, money and cell phones
.
The reason US phones are larger is because a smaller phone won't work. The lower US population density means a more sparse cellular network, which means a longer (on average) radio link, which requires more RF power. Better frequency filtering can help some, but there is a fundamental limit (described by the Shannon-Hartley theorem) to how low the power can go. The main reason phones have gotten smaller in the last 5 years is because continued build-out has made the networks denser.
Simply put, a ring-size phone is just plain impossible with anything remotely resembling current physical plant and battery technology.
The proper question is does the technology use tantalum, which is the useful part of coltan.
Funny thing... Africa isn't the major producer of the stuff. Australia is, then Africa, Brazil, Thailand, China, Canada and Malayshia.
I doubt that a slower, more expensive and more highly breakable technology is going to bereplacing the current one. A general rule of thumb is that no moving parts can be faster/safer/lower power/smaller than moving parts.
I think you're confused about what the "moving parts" are and what they do. Those rules apply to moving parts that rub against each other. These devices are resonators and diplexers, implemented as parts that vibrate and flex, like a bell ringing or a tuning fork humming.
Matter flexes all the time, regardless of whether the motion is deliberate or just a response to heat. Unless the flexing is so large that atoms are displaced from their resting place they don't wear out for geological time.
(Even some displacement is possible without wear. It's called "annealing". Atoms move around slightly to release stresses, resulting in a part the same shape but less brittle.)
For a resonator: In place of electronic tuned circuits (capacitors and inductors, with the action taking place in the motion of electrons and the electric fields between, and magnetic fields around, large conductive structures) you use nanoscopic tuning forks or other shapes with sudden discontinuities.
The motion of electrons through long circuits at about 2/3 the speed of light is repaced by the motion of atoms through distances comparable to their own diameter, at speeds more typical of large masses pushed by moderate forces.
The electric field between two metal plates is miniaturized as the electric fields between pairs of atoms.
The "inertia" of the magnetic field around a long conductor is replaced by the physical inertia of moving atomic nuclei.
The operating speed is EXACTLY the same, as is the amount of energy used. (For a given "Q" factor the friction losses are the same, whether a tuned circuit is implemented as an electrical or nanomechanical structure.)
This kind of thing has been done before - about the time transistor radios became pocket-sized. One example is a miniature quartz crystal about the size of a large ant, precision cut and with precision-deposited electrodes and "doping" weights, replacing (and doing a better job than) about a half-dozen tuned circuits, each pair about the size of a pencil eraser.
But that was for a frequency under half a megahertz. Now we're talking several factors of ten faster - which translates to several factors of ten smaller. And we're now in the range where we can replace several tuned circuits the size of the chip with several silicon and metal structures each about the size of a large transistor.
As for "expensive" to construct, we're not talking microscopic robot arms mounting tiny levers and wheels on axles. We're talking etching a shape into silicon, glass, or conductive metal. This can be done using the same processes that put the circuitry and interconnections onto the chip. (It might not even take any extra steps.)
Bantam Dominique roosters crow a four-note song. Once you've heard it as "Happy BIRTHday" you can't NOT hear it that way
You are misunderstanding how this works -- it doesn't help that the reporter evidently didn't understand either. The article didn't say this, but it's obvious that the proposed MEM filters are for the receiver circuits, not the transmitter or speaker circuits where power capacity is an issue. (Forget the ring phone, other posters have cited many reasons it's not going to happen.)
Presently, the most precise analog input filters are electromechanical devices called SAW filters. An array of electrodes apply the input signal to start a piezoelectric crystal vibrating, with another array picking up the output signal. The signal passes through the crystal as a sound wave; the crystal might oscillate at many frequencies, but to pass between crystal and electrodes, the sound wavelength must match the array spacing.
The proposed "MEMS" filter is a tuning fork etched out of semiconductor, I assume with piezoleletric input and output electrodes. Only signals at very near the natural oscillation frequency of the fork can set it vibrating so as to be picked up at the output electrode. The electrodes can be much smaller, and for cell phone frequencies obviously the fork has to be very tiny. Since the device is smaller, it doesn't use as much power.
"Slower" -- no. "Uses more power" -- no. "More expensive" -- true for now, but the tinier device will probably be cheaper once it's become a commodity part mass-produced in competing factories. "More breakable" -- yes, but I don't think it will be breakable enough to be a likely point of failure. A really strong shock in the right direction could snap the tuning fork, but considering the tiny size and considerable strength of the likely materials, you'd probably mangle the case, display, and circuit board before you damaged the MEMS.
A slightly more realistic reliability concern is that for a tuning fork to work, it has to have air space around it. That is, where solid-state components are encased in solid epoxy, a bubble would have to be left around the fork. It's OK if the bubble comes out the intended size and location, and the epoxy covers it completely and makes a good seal around the wires. But if there's the slightest leak to let moisture or anything else get into the bubble, the device will soon die. There are a few larger components which require air bubbles to operate: crystal oscillators usually have a tuning-fork in a bubble, some optocouplers have an air gap separating the LED and phototransistor. No matter how much effort the manufacturer of these devices puts into controlling the build process and testing them 100%, we always have a few go bad when we solder them to the board. They also tend to have high field failure rates, although I don't know if that is due to leakage into the bubble. Crystals are lower frequency and a larger tuning fork, so more breakable, and optocouplers are used mainly to prevent high voltage zaps from getting into the device -- it's no surprise when a device that's _expected_ to be zapped gets zapped too much and fails.