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  Date: 19/02/2013

ADI's chip Guru speaks to EEHerald on analog, 3D IC, and MEMS

In the analog semiconductor world, anybody who care for utmost precision could not have designed (mostly) any system without using ICs made by Analog Devices Inc (ADI). Though there are many analog vendors with high performance analog IC product offerings, Analog Devices leads over competitors in performance in some of the important categories of Analog semiconductor ICs.

Analog Devices focuses exclusively on high-performance, where the boundaries of precision are always pushed. This writer could able to meet analog and mixed signal tech guru Dr. Samuel H. Fuller, Chief Technology Officer at Analog Devices. Below is what he says to some of the queries on silicon technologies:

Q: We know Analog Devices is performance focused and high precision chip maker. There is one thing called 'noise' which can't be get rid off, you are trying to give best out of market in terms of noise performance, do you foresee in the coming years the noise going down to zero?

Dr. Samuel Fuller: Noise not going to be zero. Lot of our growth going forward is in application specific standard products (ASSP). We do ASSPs with digital and analog/mixed signal part which forcibly pushed you to CMOS technologies like 65 nm moving on to 40nm and so on. When you go to lower (nodes) they have less head room for voltages and it becomes more challenging to be able to get the high performance or precision. I see a lot of our innovation is around, how do you continue to build high performance signal processing signal chains, when you are focused on using 65 nm or 28 nm CMOS.

Q: You are trying to focus on lot of integration in SOC. In SOC, there is digital as well as analog and when it comes precision analog, how much of the precision analog can go into SOC kind of chips?

Dr. Samuel Fuller: A lot of our SOCs and ASSPs are at 180 nm and we are moving to 65 nm, there is pressure that you would like to move to the denser nodes such as 28nm . There is no fundamental road block to coming up with new circuit architecture that you know work within the much lower voltage of the denser CMOS. So the Challenge is how do you come up with a new-- say, converter architecture, whether it is a SAR (Successive Approximation), Delta Sigma-- you begin to incorporate more and more digital calibration and predistortion (techniques). There is lot of innovation on what type of digital calibration is most effective when we move into deeper nodes.

Q: Using your own fab vs using semiconductor foundries:

Dr. Samuel Fuller: We have two large fabs (semiconductor) in North America and Europe and we certainly use the foundries such as TSMC and GlobalFoundries. The way we look at this is, we need the very fine lithography CMOS for digital centric products, we go into foundries. Imagine the amount of analog and linear mixed signal products which needs specialized processes either for higher voltage or higher power, so there is lot of demand for such requirements in our own fabs. We also have MEMS devices like microphones, accelerometer, gyroscopes, those again are specialized processes and we have chance in our fabs.

Q: What about the applications which require System in Package (SIP) instead of system on Chip (SoC)?

Dr. Samuel Fuller: Absolutely, we are looking more and more of these sort of system in package.

Q: Are you looking at 3D packaging?

Dr. Samuel Fuller: Absolutely, through silicon vias. The challenge that we got and industry got is to drive the cost down for building multi die packages, they are competitive, because when there is still so much of push to try to get lot out of one die to cut down the assembly cost. But in reality we think about trying to do everything on one die, you end up with a very complex processes, the multiple steps to do the very high voltage device in one step and other step to do fine line CMOS. But you can get through the silicon vias and other techniques for doing die on die and then packaging. ADI is involved in number of industrial consortiums (3D packaging).

Q: Are you trying to leverage packaging providing services from other companies?

Dr. Samuel Fuller: Absolutely, wherever we can. Things like silicon vias has to be done in the fab. So silicon vias and other processes we have to do in our own fabs and our foundries TSMC and globalfoundries are obviously innovating as well. We all involved in industrial consortiums, so as we do that, we all go to the same standards. We also buy bare die for flash memories from other vendors, and what we need is the standard way of interconnecting silicon vias from die to die, so that more easily source some of the chips for 3D packaging. So I think multi die packaging is going to be an important part of the business.

Other part of our fastest growing package is the chips that have no package, you know -- the wafer scale packaging. We are bumping the dye, passivated top, it is such a smaller footprint, it becomes attractive. some years ago nobody thought about it, now it is the fastest growing package type. (These wafer scale package devices are used in muti-die packages).

Q: On the technology of integrating capacitor and inductor inside chips:

Dr. Samuel Fuller: I think one of ADIís real strengths in our fabs are the passives. We invested a lot, we would do trimming as well as resistor-capacitor in-built through one-time programming, because we can trim them to high accuracy, then capacitors as well (MEMS caps). For inductors, there is whole lot of stories. I would say, we have got one line of isolated products which are built with inductors and its very popular line for providing good isolation in industrial application. Its called ISO line . We use inductive coupling to move the signal and some times power too.

Q: On the sensor integration on silicon:

Dr. Samuel Fuller: We started out with high G accelerometers 4 years back, later we found that for stability control we need low G accelerometers. Right now, we got a very interesting product, a medical device where accelerometer measures milli G and is capable to measure actually the pulse (heart beat). The most recent MEMS device is microphone. We are looking at the various experiments now, where we might put multiple microphone on a single die separated by few millimeters and will be able to get both directional info as well as acoustic info.

Q: How reliable are these pressure sensors made using MEMS. I mean in precision as well as the range of measurement?

Dr. Samuel Fuller: Great point! They are certainly reliable for some of the products, but there are requirements for number of applications that need to be more robust. We are looking at next generation of products, its (sensor) fundamentally has to be open to atmosphere to be able to get the pressure. Also needs some limiting factors, so that if we get some really strong acoustic shock, you donít want to break the membrane. We are working on what kind of mechanical structure can provide that same limiting factor, so that it does't get blown up. Where we go beyond that! that's where we are doing our research and development.

Q: Trend of integrated AFEs over discrete ICs:

Dr. Samuel Fuller: For very low volumes, discrete ICs in small packages makes lot of sense. Then for mid volumes, it is ASSPs, where ADI has lot of strength in ASSPs. I am most excited about our software defined radios, the RF frontend. In a single die we have both transmitter and receiver, it goes all the way from RF front end through a mixer -- through a set of ADC converters and D to A converters feeding the data to/from FPGAs. We have done all of this in 65 nm. Then we get into highvolume, we almost build ASICs, those are very demanding in terms of time schedule, synchronized with OEM schedule.

On the size trend Dr. Samuel says the 1mmx 0.5 mm (sand grain) size op-amps and other devices are in demand in mobile applications.

On India development office, Dr. Samuel says "10 % of our design talent is in Bangalore. We have a lot of small design centers around the world in Europe and US. This over here (India) is going to be one of the principle design center"

Pic below: Dr. Samuel Fuller
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