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28nm FD-SOI: Samsung & ST's Major Opportunity

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AKH0
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Re: 28nm FD-SOI
AKH0   7/26/2014 1:25:48 AM
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IBM's 22nm which is used for power8 is PDSOI, which is very similar to bulk planar in terms of scaling and in fact uses a gate length shorter than Intel's 22nm FinFET. Samsung and others made 20nm bulk planar and showed their results. ISDA's 20nm was shown in at VLSI 2012. TSMC is said to ship 20nm parts this year. The problem with 20nm was not scalability, it was cost. For your information foundry's 20nm uses 64nm metal pitch vs Intel's 80nm. Which means foundry is offering a denser technology, which of course comes at the cost of double patterning. FDSOI products have already made by ST, see for example NovaThor demo in early 2013 that clearly showed SOC benefit. Samsung is now committed to offer 28FDSOI to the public. I do not understand your repeated comment about 28nm bulk planar being in high volume for several years as a drawback of FDSOI. Yes, 28nm has been in production for several years, but it didn't come with all bells and whistles at the beginning. The first products used poly SiON gate stack and no strain element to keep cost down. Overtime several versions of the technology with different cost-performance trade offs were offered. They are put into volume manufacturing when fabless companies demand a certain performance and are willing to pay for that extra cost. 28FDSOI is no exception to this. Volume manufacturing was put on hold because customers did not demand. BTW, Intel's 14nm FinFET is not in manufacturing yet and there has been multiple delays. And there is no such thing as "end of roadmap". Technology is scaled as long as it makes financially sense to do so. Whether it's being conventional scaling of the transistor, being stacking in 3D, or a completely new technology the same way BJT was replaced by MOSFET logic.

michigan0
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Re: 28nm FD-SOI
michigan0   7/26/2014 12:37:42 AM
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Sang Kim

 

The 28nm planar bulk has retrograde and halos as you pointed 

out, but ends at the 28nm node. FDSOI is worse because 

FDSOI is not manufactured at any technology node yet as I

pointed out in my original post. Intel, IBM, TSMC and others 

attempted to extend the planar bulk to the 22nm node, but 

were not successful because of the short channel effect or 

unable to suppress transistor leakage current. Intel finally 

developed its first FDFinFETs at 22nm, and its 14nm FinFETs

are in high volume manufactured today. FinFET technology  

can be extended to the end of roadmap.



AKH0
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Re: 28nm FD-SOI
AKH0   7/23/2014 7:06:20 PM
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No, the doping is not uniform in bulk planar! The well is retrograde (although not ideal) and there are halos. The whole point is that the well and halo doping will take care of leakage at the depth and gate takes care of it at the surface. I agree with you that the ideal supersteep retrograde will end up with high drain leakage, but that's not the case in FDSOI because drain is isolated from the substrate by the BOX.

BTW, your point about Vt being higher and more variable in a retrograde well is not correct either. In fact it's the other way around! Please see page 230 of Taur and Ning's text book. With retrograde well design Vt is lower than a uniformly doped well and in the extreme case independent of the well doping. This is in fact what SuVolta is promoting. Of course, with Vt being independent of the well doping you cannot use Vt adjust anymore and need to rely on body bias. What FDSOI does is simply making an ideal retrograde well possible and allowing the well doping to have either n+ or p+ polarity for either NFET or PFET witout fearing about drain leakage.

 

 

 

 

 

 

michigan0
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Re: 28nm FD-SOI
michigan0   7/23/2014 6:39:41 PM
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Sang Kim

 

28nm planar bulk that is in mass production today for several 

years has uniform doped substrate that provides a fixed Vt  

and fixed depletion depth determined by uniform substrate 

doping. In a bulk planar device with super steep retrograde 

well, Vt could be higher and variable, and the gate depletion  

is blocked by the well doping, not by current flow. The current 

doesn't flow in the well unless hot carrier effect. The current 

flows from source to drain. Furthermore, the drain electric

field will be significantly higher in the retrograde well. As a 

result, hot carrier induced device failure could be higher.

 

First, the planar FD-SOI is not manufactured at any technology

node yet. Why? The un-doped 28nm FD-SOI requires an ultra-thin SOI channel, for an example, a 7nm for 28nm FD-SOI. My 

question is how the ideal super steep retrograde process can

be implemented in the 7nm thin SOI channel? It appears that

the un-doped planar 28nm FD-SOI is stilll not manufacturable.




AKH0
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Re: 28nm FD-SOI
AKH0   7/22/2014 12:07:43 AM
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In a bulk planar device with super steep retrograde well, gate only needs to control the top portion of the substrate. Current flow is blocked at deeper locations by the well doping. Similarly in the planar FDSOI gate only needs to control current flow in the SOI layer, below that current is blocked by the BOX. You can imagine an ideal super steep retrograde well device as being to be equal to an FDSOI device with a BOX thickness of zero. Would you say such a device will suffer from pinch through?

michigan0
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Re: 28nm FD-SOI
michigan0   7/21/2014 8:29:49 PM
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Dear AKHO

 

Thanks for your comments 

 

Bulk planer device has shallow implant combined with retrograde 

deep implant to prevent punchthrough regard less Vg is on or off. 

What do you mean by top 10~20nm is depleted? Intel FinFETs 

also have PT implants. Here we are talking about un-doped 

FD-SOI.



AKH0
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Re: 28nm FD-SOI
AKH0   7/21/2014 4:51:07 PM
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Dear Sang Kim

At Vg=0, the channel is fully depleted, whether it is in a planar FDSOI or in a FinFET with reasonably low doping. Even in a bulk planar device the top 10-20nm is depleted. That doesn't mean a well-behaved device is in punchthrough wheter it being FDSOI/FinFET/or bulk planar. Your way of describing what seems to be physics is incorrect. I would recommend you consult a text book. Punchthrough happens when gate significantly loses control of the channel and high current folows independent of the gate voltage. This is certainly not the case in all the I-Vs that have been published for sub-30nm gate length FDSOI devices. Drain-induced barrier lowerin (DIBL) is of course inherent to any short channel devices and you CANNOT make it zero. In fact I will argue it does not makes sense to make it smaller than about 100mV/V either.

 

Your assumption of the gate length needed for a given technology is also incorrect. Gate length has nothing to do with the technology node (and it didn't in the past). At 28nm, FDSOI is using a gate length of 24nm, which is shorter than any alternative at the same node. At 14nm, gate length will be most likely 20-22 nm and so is at 10nm. All needed from gate length is that it fits the required gate pitch and the numbers I quoted above fit the bill perfectly.

Finally, the rule of thumb requirements of the channel thickness for a given gate length are just guidlines. Many other parameters such as gate stack, junction design and BOX thickness affect the electrostatic of the device. This is also the case in FinFET. No one needs 3nm SOI for 14nm FDSOI.

 

 

 

 

 

michigan0
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28nm FD-SOI
michigan0   7/13/2014 1:48:51 AM
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Sang kim

 

Handel Jones says 28nm FD-SOI is an alternate option 

for low leakage, high yields and high performance superior 

to 28nm bulk technology. Consequently, Samsung

can support low leakage products with its 28nm FD-SOI.

look at the real issues with FD-SOI. My first question is why 

28nm FD-SOI is still not manufactured today by major 

semiconductor companies because 28nm bulk is manufactured 

for several years by major semiconductor companies today 

such as Intel, TSMC, Samsung and others. 

 

In un-doped FD-SOI channel here, it is possible for drain depletion to extend with large Vdd(1V) to source without inversion. I call this effect punch-through. Therefore, punch-through failure can occur in un-doped FD-SOI. On the other hand, the drain induced barrier lowering or DIBL leakage current most likely occurs also in un-doped FD-SOI. In order to prevent such DIBL leakage current it is imperative to have an ultra thin SOI channel layer between source and drain so that the drain field can't easily penetrate the ultra thin SOI channel. How thin the ultra thin SOI thickness has to be in order to stop DIBL leakage current? It depends on the channel or gate length, Lg. For shorter Lg, a thinner SOI  channel is required. This is the most critical issue for FD-SOI.

 

For 28nm FD-SOI a 7nm thin SOI channel thickness is required to stop DIBL leakage current. However, the transistor performance becomes significantly degraded due to the transistor mobility degradation because of scattering of charge carriers at the top gate oxide surface and at the bottom SOI surface in the 7nm thin SOI channel. As a result, even if 28nm FD-SOI were manufactured today, it wouldn't be superior to 28nm bulk in terms of transistor performance and manufacturing costs due to significantly higher SOI wafer costs. These are the major reasons why the 28nm FD-SOI is not manufactured today.

The other major issue with FD-SOI is its scalerbility. For

20/22nm FD-SOI a 4~5nm SOI channel thickness is required

to stop DIBL leakage current thus further degrading transistor 

mobility. Furthermore, it is extremely difficult to control 4~5nm 

SOI channel thickness uniformly and reliably across 12 inch 

wafers in the manufacturing line. How thin SOI channel 

thickness is required for 14nm FD-SOI technology? 3nm! It 

appears that FD-SOI is not scalerble. 

 





AKH0
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Re: 28nm FD-SOI
AKH0   7/13/2014 1:32:21 AM
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Dear Sang Kim, I am not sure what you mean by punch through. There is no leakage path other than the thin channel which is fully controlled by the top gate. I-V characteristics of FDSOI devices have been published in major conferences and there is no sign of degraded electrostatic as you claim. As far as the mobility degradation in thin SOI is concerned, mobility is already hit by high-k gate stack and yet every body is using it. As far as a device delivers the performance why should I care if mobility is higher or lower. Let numbers speak for themselves. We have shown 1.65 mA/um at 1V and 100nA/um for NFET which as far as I know is the highest DC performance ever reported. For PFET drive current is 1.4 mA/um which is again record high. And these are devices at pitch with all parasitic resistances of real technology. And unlike FinFET camp there is no cheating in drive current normalization. I do not want to brag about DC performance as there are many other factors determining circuit performance. But if you are concerned about DC performance please take a moment and review papers in the past few IEDM and VLSI.

HJ88
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Cost Per Gate is a Critical Factor
HJ88   5/20/2014 6:39:59 PM
The cost for 100M gates of a product made with 14nm FinFET (including 16nm FF+) will range from $1.38 to $1.53 in Q4/2016.

28nm HPC cost per gate will be $0.97 for 100M gates (28nm fab partly depreciated).

For 28nm FD SOI (even allowing for the high cost of the substrate), the cost will be $0.92 for high volume manufacturer. Margins have to be added to get wafer prices from the foundry vendors.

For the high volume applications, cost is the most critical factor followed by power consumption.

The reality is that TSMC and Samsung are very close in their road maps for trying to ramp 16nm FF+ and 14nm FF. While process control is a key factor in bringing up FF products, another critical factor is DFM and impact on parametric yields. It is low parametric yields that have delayed the ramp-up of 14nm FF to date.

Cost per gate is a critical factor, and longer term cost and price do have a relationship.

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