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The new self-sustaining sputterer uses a metal plasma instead of a noble gas one. The metal plasma glows green in this picture, while the metal ion source glows white as it emits ions.   (Source: Lawrence Berkeley National Laboratory)

A traditional sputterer uses a magnetic field between a target semiconductor (thick brown disk, bottom) and a metal ion source (brown, top). A plasma gas such as argon (pink) knocks ions, neutral atoms off the metal (brown dots), and electrons (white) off the metal source, yielding a metal layer on the circuit.  (Source: Lawrence Berkeley National Laboratory)

The new method improves this power by adding more power, which allows it to do away with the argon and create a self-sustaining pure metal plasma (brown dots are metal ions, white are electrons). This metal ion plasma deposits a virtually voidless layer, allowing high-performing nanoscale circuits to be easily produced.  (Source: Lawrence Berkeley National Laboratory)
New sputtering approach allows nanoscale deposition, new ion engines

Metal interconnects and features are a critical component of modern silicon circuits.  In space, NASA and other space agencies have prototyped new ion engine technologies which promise more affordable and faster propulsion to distant targets.  What both technologies have in common is the need to create ions to drive their key processes.

Researchers at the U.S. Department of Energy Lawrence Berkley National Laboratory have devised an improved method to produce more metal ions, allowing it to create better circuits, and unlock other applications.

Metal ion creation in the semiconductor industry relies on a technique called sputtering.  Traditional sputtering relies on a gas such as argon being heated to plasma and then contained by a magnetic field between a layer of metal and a target circuit.  The plasma knocks metal ions off the metal source, creating a current of metal ions which flows towards the circuit, depositing metal on the disk.

High Power Impulse Magnetron Sputtering (HIPIMS) was invented in the 1990s as a means of improving this process.  It uses a more powerful magnetic field to accelerate the plasma to higher speeds and to allow some metal ions to return to the metal source, knocking off more metal ions in a chain reaction of sorts.  They key limitation to this process was power.  More power means better performance, but in commercial semiconductor production typically only 1 kW magnets can be used, and they require water cooling.  The result is a sputtering process that is not self-sustaining, though it last slightly longer.

Researchers at LBNL believe they have created the world's first self-sustained sputtering process.  Their key is to use high power impulses, rather than a steady higher current, which could melt the magnet. 

Andre Anders, a senior scientist in Berkeley Lab’s Accelerator and Fusion Research Division, describes, "Three quantities determine the self-sputtering threshold.  One is the probability that a sputtered atom gets ionized. Another is the probability that the new ion returns to the target. Finally, there’s the actual yield of atoms from self-sputtering. Multiply these together and you get the self-sputtering parameter, which is symbolized by the Greek letter pi.  When pi equals unity, you reach a new steady state (provided) that the power supply can keep up.  We use a special power supply, up to 500 kilowatts peak power. If the system wants power, we give it power!"

The process is also unique in that the power is high enough that it can create a thick plasma of pure metal ions, eliminating the need for argon or other gases in the sputtering process.  The result high power continuous sputter has many benefits including cost cuts in chemicals, better circuits, and less mechanical parts (by removing the need for gas injection).

For very small circuits, that will soon arise as die shrinks continue, depositing metal using previous methods might be infeasible as they leave regular voids that on a nanoscale could break connections.  With the new approach, the thicker metal ion plasma yields in essence void less deposition, allowing for nanoscale designs with excellent electrical character.

Another potential use of the new sputterer is in spacecraft.  Bottles of gas or liquids are bulky and ultimately increase weight by requiring more metal to enclose their greater volume.  A metal ion source, using the new method would be self sustaining and much more compact, lowering the weight and cost of launch for ion engine powered spacecraft.

The method also works in a vacuum, so it could also be used for metal ion sputtering in spacing, aiding orbiting construction platforms one day.  The method could also be applied on Earth to allow for the first ever successful sputtering of niobium, a tough metal to sputter.  This would allow for superconducting cavities of future particle accelerators to be coated with this metal for improved performance, unlock a plethora of new research possibilities.

In short, the new self-sustained sputtering method is a breakthrough which will help advance a number of fields, and if properly implemented, should become an integral technical advance of the new century.



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RE: Great article!
By Triple Omega on 2/2/2009 7:03:24 PM , Rating: 2
Sustaining a nuclear fission reaction safely here on earth in a very comfortable environment with permanent monitoring and maintaining from an expert staff is one thing. Doing it on an autonomous spacecraft (that first has to be launched violently into orbit) moving through the hostile environment of space with no humans around to monitor or maintain anything for years or even decades is a whole other matter.

I know that self-sustaining nuclear fission could be possible in the future, but to do it in space would be extremely hard. Just look at the amount of technical failures that occur in space right now. Taking into account the fact that nuclear fission is a delicate process, a failure of a critical system during any of the many years of travel would be devastating and there are a lot of things that can go wrong out there.


RE: Great article!
By 9nails on 2/2/2009 8:00:30 PM , Rating: 2
That's especially true considering that "Space rated" computer processors are like IBM PowerPC 25 MHz CPU's. The problems created by extreme heat, cold, and radiation make a faster processor unfit for space. You couldn't have too robust of a computer monitoring program maintaining this engine. They would also consider the lag time between Earth and the ship/probe in respect to human intervention; it could take hours before manual corrections are made.

In Space, it's not unheard of to have failures even in triple redundant systems. That fission system would need to be bullet-proof if they want to ensure arrival. This sounds like a wonderful engineering challenge!


RE: Great article!
By MrPoletski on 2/3/2009 7:05:54 AM , Rating: 2
sounds like a SIL 4 application then.


RE: Great article!
By masher2 (blog) on 2/2/2009 10:12:57 PM , Rating: 3
quote:
Doing it on an autonomous spacecraft [with] no humans around to monitor or maintain anything for years or even decades is a whole other matter
Even a 1970s-era nuclear reactor doesn't require a large amount of human oversight, except for operations like refueling. With new advanced reactor designs and, even more importantly, advances in computer monitoring, there really isn't any need for humans in the loop at all.

Furthermore, I'm not sure why you're assuming an unmanned flight in the first place. We can already build deep-space probes using ultra slow Hohmann transfers and gravity slings...you need nuclear propulsion for fast manned missions.


RE: Great article!
By Triple Omega on 2/3/2009 6:25:29 AM , Rating: 1
quote:
Even a 1970s-era nuclear reactor doesn't require a large amount of human oversight, except for operations like refueling. With new advanced reactor designs and, even more importantly, advances in computer monitoring, there really isn't any need for humans in the loop at all.

Again even if this is true, it is true on Earth not in space. Compared to space the Earth is a VERY comfortable environment to operate a nuclear fission reactor in. In space, computers can fail(even permanently due to radiation), which could be disastrous if normal operation doesn't resume quickly, cooling equipment can fail(with no-one around to do anything about it), etc. So doing something on Earth without problems doesn't mean you can do it in space.

quote:
Furthermore, I'm not sure why you're assuming an unmanned flight in the first place. We can already build deep-space probes using ultra slow Hohmann transfers and gravity slings...you need nuclear propulsion for fast manned missions.

I'm assuming an unmanned mission for two reasons:

1) Since it isn't the cold-war era anymore, I don't think anyone would risk letting the first multi-year test be a fully blown manned mission. Besides the risk for human life it would also be very politically risky. If it blew up mid-mission that surely would damage the reputations of both nuclear powered flight and the space agency.

2) Nuclear powered flight isn't just useful for manned missions. Unmanned (deep-)deep-space missions will also need to be nuclear powered if we don't want to wait decades or even centuries for a probe to get anywhere.


RE: Great article!
By masher2 (blog) on 2/3/2009 10:05:02 AM , Rating: 2
quote:
Unmanned [missions] will also need to be nuclear powered if we don't want to wait decades or even centuries for a probe to get anywhere.
Sounds like you're admitting the need for nuclear propulsion.

quote:
In space, computers can fail(even permanently due to radiation)
We've come a long way with radiation-hardening of circuits. But still, yes this is a serious concern.

However, you might want to look into recent developments in magnetic shielding, by a method analogous to the earth's relatively weak magnetic field which, however, shields us all.


RE: Great article!
By Triple Omega on 2/5/2009 5:22:26 AM , Rating: 2
quote:
Sounds like you're admitting the need for nuclear propulsion.

No, I'm admitting the need for nuclear fission propulsion for deep-space probes at this time. That doesn't mean we have to use it now. We could try to develop other techniques to prevent the use of nuclear fission or we could opt to make nuclear fission use in space much safer first. Just because something is the only way right now doesn't mean we HAVE TO do it.


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