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Medical ASICs: What’s Next in Silicon Integration?

Medical ASICs, particularly for the portable and implantable device market, are largely driven by the need to reduce size, weight, and power. The general tendency is to think that more integration is better. As my colleague Andy Kelly blogged recently (Medical Device ASIC Integration: Optimize, Don’t Maximize), blindly integrating all analog, digital, and RF on a single piece of silicon (called a System-on-Chip or SOC) may increase development time and risk, reduce system flexibility, and compromise performance.

However, silicon integration may reach far beyond the traditional questions of whether to integrate digital, analog, and RF on one integrated circuit. So what's next for silicon integration? Perhaps more importantly, what types of integration will provide the most benefit for devices such as those used in portable and implantable medical?

In discussions with our customers as well as a review of their overall electronic and mechanical systems, there are some clear areas to examine with regards to future silicon integration. A generic system consists of a sensor/transducer, integrated circuit(s), power source, and passive devices including mechanical devices such as connectors. Interestingly, many of these devices are now being implemented in silicon processing technology similar to ASIC technology. This obviously raises the question, “Why not integrate all these devices onto a single piece of silicon?” Let's look at each of these devices in a bit more detail.

Sensors

Sensors have already become significantly smaller with the advancement of micro-electro-mechanical devices called MEMS. MEMS are using silicon wafer processing capability to create miniature accelerometers, pressure sensors, gyroscopes, touch sensors, and other electro-mechanical devices. In the past, MEMs were offered discretely as a separate die or packaged device.

However, now we see the MEMs devices being offered as part of standard CMOS IC processing to provide a more fully integrated solution. For example, X-Fab provides its foundry customer access to relative and absolute pressure sensors on their XC10 and XH035 IC technologies at the cost of only one additional mask. This reduces chip-to-chip interconnect and overall system size.

Passive Devices

Examples of electronic passive devices found on a printed circuit board might include capacitors, resistors, and inductors. These devices are discrete components that are often not integrated in an ASIC due to size or performance requirements. For example, microfarads of capacitance might take an unreasonable amount of die size if integrated. Similarly, a large resistor value or a resistor of acceptable tolerance (10 percent or better) might not be achievable in standard integrated circuit processing.

However, today newer IC technology is available that focuses on integration of passive devices. For example, On Semiconductor's Integrated Passive Device (IPD) technology allows for integration of copper inductors, precision resistors, and precision capacitors. Capacitor density of 100nF/mm2 with better than 10 percent tolerance is available. If you examine the PCB of an implantable medical device that requires a boost or buck converter, the inductor alone is a significant consumer of real estate. If the inductor can be integrated into an IPD chip, substantial size reduction can be achieved.

Power Source (Battery)

Implantable medical devices usually, although not always, make use of a battery that is resident with the implantable device. These batteries come in two flavors, a primary cell (used once), or rechargeable cell. Relatively new rechargeable solid-state batteries (SSB) are now readily available (Cymbet Corp.). To date the primary issue with solid-state batteries has been battery capacity. A single cell might provide 6-12μA-h of capacity. Compare this to typical coin cells with capacities in the mA-h.

But these SSBs have an important advantage — they can be stacked and connected in parallel to provide higher capacity. Solid-state batteries are fabricated on silicon wafers using the same standard semiconductor processes and equipment. The device functions much like a standard rechargeable Li-Ion battery with significant space savings. Today the batteries can be purchased in standard IC packages or in bare die form. If purchased in bare die form, the batteries can be used as part of a multi-die stack to increase integration.

However, according to Jeff Sather of Cymbet, in some medical applications x, y, and z dimensions are so constrained that even a die stack is too big. Thus full integration might be necessary. Currently for very small SSB, and for medical applications in particular, a fully integrated approach can be technically and economically feasible.

Conclusion

Standard implantable medical devices are relatively large, with device volumes occupying between 15cc and 50cc. In order to reduce size and produce devices that can be placed at the point of therapy with less invasive surgeries we need to reduce their volume to less than 4cc. These miniature implantable medical devices (MIMD) must leverage higher levels of integration to meet this goal.

Relatively new technologies are leveraging silicon wafer processing methods and silicon wafers substrates to make various system components such as sensors, passive devices and power sources smaller. Therefore it would seem reasonable to assume that such components could eventually all be integrated onto a single piece of silicon. However, as my colleague has pointed out, we need to understand the trade-offs in the quest for a fully integrated solution. “Smart integration” should win out over “maximum integration” every time.

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32 comments on “Medical ASICs: What’s Next in Silicon Integration?

  1. fasmicro
    September 18, 2013

    The really exciting thing about medical ASIC is that not everyone can get into that business. It is one that can send a company to bankruptcy. It is extremely specialized and dangerously opportunistic. You can sell a gyro $40 to a medical device maker and to a consuler product firm you cannot get a gyro for $1. Integration is becoming a norm there and MEMS is helping in that regard. 

    Yet, medical ASIC is not a consumer ASIC – it is a different beast. Integration is the hope as they look for how to pack more stuffs inside a small size.

  2. Netcrawl
    September 19, 2013

    @fasmicro I agree with you, its a kind of business that require core competencies and brutal discipline, medical ASIC is a different story, its far more complex compared to consumer ASIC.

    In today's challenging environment ASIC provides a huge boost, it incorporates a large amount of functionalities into small custom-made IC, Its an highly intelligent stuff that remind you everything like taking a pill, monitor your blood sugar, check your blood pressure and even inform your physician that you're running out of something.   

  3. James108
    September 19, 2013

    The custom medical ASIC market, particularly the implantable side, is indeed a challenging business.  In addition to the liability concerns with a life sustaining ASIC, the product volumes on the implantable side are usually quite small and the time to market and production revenue is very long (FDA approval). 

    As such the unit prices are indeed higher as you indicated.  To be successful you need to really think about your business model and each customer engagement.  It is very helpful when your medical customer also understands the custom medical ASIC business. Working together you can create win-win situations.  In reality, if you absolutely need to minimize size and power (or you have no product), a custom ASIC is going to move you closer to an optimum solution. 

  4. Davidled
    September 19, 2013

    This kind of technology is much closed to government as a big sponsor.  All IP and technology belong to them. In the future, engineer of government might upgrade for other purpose in biomedical engineering Lab.

  5. Netcrawl
    September 20, 2013

    @Daej what do you think do we need to include some bio sciences subjects in our engineering course? I guess we would need that, it getting tough in the medical industry- it require some good knowledge of human science. And we're not medical people, we're engineers we're not trained for this stuff.    

  6. James108
    September 20, 2013

    As a semiconductor company, it is usually our customer, the medical device companies, that have the Biomedical engineers on their staff.  In addition, those customers are working closely with the doctors and/or patients to define real needs of the end user.

    As integration levels increase, we clearly see the need for teams across different disciplines to be working together, especially early on during the product definition stage.  As we pack more into silicon and try to reduce overall device size while at the same time meeting the needs of the end user, we clearly need inputs from many different vantage points. 

  7. eafpres
    September 20, 2013

    Hi James–thought provoking article; thanks for thoughts from someone in the busienss.  As others have stated there is a real challenge that you benefit if your customers, who are chemists, biochemists, chemical engineers, cellular biologists, and the like, understand the medical ASIC business.  I would think that likewise, you could benefit from understanding their world.  Clearly someone in your position has that cross cutting knowledge, but it is a real challenge down at the design level.

    Back when I received my BS in Chemical Engieering, many ChE grads went into very different industries than traditional oil, petrochem, etc.  The reason was that ChEs tended to have broader knowledge with the benefits of an engineering education.  At that time (I'll just say “in the 80s”) however, it was common for ChEs to take 5 years to get a BS degree, due to the breadth of coursework and a tendency to add on even more than the requirements.  Today, with pressure to make education affordable, and pressure to get out of school and earn to pay off your debt, I'm not sure how many students not headed for an MS or PhD will go for 5 years.

    What do you think about broadening curriculum in things like EE to increase the application knowledge space of designers?

  8. eafpres
    September 20, 2013

    Hi James–I was wondering what applications can get by on such tiny batteries.  Do you see the main applications as being temporary devices, such as targeted drug delivery nano-devices, or sensor pills that must last a couple days after swallowing?

    Right now energy harvesting is just getting pretty real for wireless sensors and sensor networks.  Using MEMS devices you can generate power from mechanical motion of the human body.  I've seen suggestions to use the motion of the heart to provide recharging of pacemaker batteries.  Do you see energy harvesting via MEMS as something of interest in your customers, and do you think it will someday be integrated into small SOCs for implantables?

  9. Netcrawl
    September 20, 2013

    Its limited and lack some functionalities @easpres, power still a major issue in implantable device. Then another one, it's on nanotechnology how to get smaller but good enough to fix everything on board( this is exactly what nanotechnology should do for us).

    Talking about sensors, sensors have become much smaller, less expensive and low power in the last few years, driven in part by advancement on MEMS, for years people have used wireless communication to communicate data from sensors with mixed results. Traditionally these communication links have been point to point and line-powered with time-varring reliability due to some interferences.

    There's  a number of phenomena that can prevent a transmitted data packets from reaching its target destination. Its interferences, the single biggest challenges in wireless network.  

  10. fasmicro
    September 20, 2013

    >> To be successful you need to really think about your business model and each customer engagemen

    In nearly all the cases, medical ASICS are not shopped in the open market. The device maker engages the ASIC designer to develop for them. That engagement is the most critical aspect of this business since the ASIC designer does not want liability and the device maker does not understand what you do inside ASIC

  11. fasmicro
    September 20, 2013

    Education is one area where everyone knows what is wrong but cannot go ahead and fix it because of regulations. It is like asking someone to spend three years for law school – just to read through old cases in the 3rd year. Education is broken and will surely be redesigned in the next few years.

  12. fasmicro
    September 20, 2013

    >> Using MEMS devices you can generate power from mechanical motion of the human body

    In the industry and I have worked on some of these products, the energy harvested from the body is never enough. Notice that most times the people that need these implants are not the most mobile people. Some stay in beds all day and that limits the ability to generate that energy

  13. Netcrawl
    September 20, 2013

    This is exactly what competition requires to us, it want us to go deeper and innovate more, how can we innovate if we dont have enough manpower and skills. Manpower that will help us achieve our goal. Its a fusion of talents from different vantage points, you integrate some good talents into your workforces, enable you to sustain more innovation and make a breakthrough. Its really a strange things to see a bio medical workers working inside a semiconductor company.   

  14. fasmicro
    September 20, 2013

    >> ( this is exactly what nanotechnology should do for us).

    When will this nanotechnology deliver? I have been waiting especially with regards to the implantables. Nano on paper and in theory has a real prospect to disrupt the ecosystem but it is taking very long to come to market. I have expected that we will have a battery via nanotechnology to change the dynamics of this trade.

  15. fasmicro
    September 20, 2013

    >>  Its really a strange things to see a bio medical workers working inside a semiconductor company. 

    That is still better than chemical engineers running banks. Yes, that is becoming common for young engineers to move to Wall Street where they can be paid more of course. Biomed nevertheless has something to offer in a semiconductor firm. There courses are as medical as electrical.

  16. Davidled
    September 20, 2013

    I knew that there are some courses related to bio engineering program in graduate school. They might teach some course similar to bioscience as basic course. But in undergraduate program, student might not take bioscience, because this course might be required for pre-med student, not engineering students in most case.

  17. James108
    September 21, 2013

    I was in college way back in the 80's.  Many universities only offered a Biomedical Engineering program via the Chemical Engineering track.  Today many schools offer a pure Biomedical Engineering Degree.  I believe this education provides a broader look across many engineering disciplines with an opportunity to focus a bit more in the senior year.  So if you want to focus a bit more on the EE or ME side you have that opportunity.  I am amazed at the breadth of knowledge that some of the Biomedical Engineers exhibit.  Of course, the engineers I am working with also have significant work experience to go along with their education.

    As far as Electrical Engineering goes, other than perhaps an elective or two, I think you are right, it would take another year to get a significant broader background.  I'm not sure how many engineers would spend the additional year for all the reasons (many financial) that have been mentioned. 

    What I have seen in practice, is starting circuit designers work at the basic block level, think amplifiers.  As experience increases they move into higher levels of design, sub systems and eventually full integrated circuit technical leads.   Eventually some move away from transistor level design and work at the architectural definition stage. Their system knowledge grows at each step along the way. By necessity, they begin understanding the mechanical, chemical and even the human engineering aspects of the design in order to architect the best electronic solutions.  So the education comes via on the job training and, perhaps somewhat important these days, with a paycheck.

     

  18. samicksha
    September 21, 2013

    When we talk about power specially for Medical ASIC whats come to my mind is Low Drop Regulator and specially for mobile and portable products like glucose meters, insulin pens and personal heart-rate monitors.

  19. samicksha
    September 21, 2013

    Any suggestions on Multi-Project Wafers, seems good method of obtaining low cost prototypes.

  20. eafpres
    September 24, 2013

    @fasmicro–“Notice that most times the people that need these implants are not the most mobile people. “

    This is a very good point!  A good example of needing to be close enough to the application to understand such a nuance.  

    While considering your good remarks, I wondered what movement could be available from an immobile patient.  It seems that breathing must always be going on, even if with assistance.  Perhaps in the future some nano-device can be made to catch a little energy of the airflow moving back and forth inside the airway.

  21. eafpres
    September 24, 2013

    @fasmicro–“When will this nanotechnology deliver? I have been waiting especially with regards to the implantables. Nano on paper and in theory has a real prospect to disrupt the ecosystem but it is taking very long to come to market. I have expected that we will have a battery via nanotechnology to change the dynamics of this trade.”

    I think the perception of progress in MEMs and other nano-technology depends on where you look.  There are printed batteries, for instance.  But on their own they would not be appropriate for an implantable device.  One of the largest MEMs markets is in phones, where accelerometers are nearly standard, some MEMs microphones are widely used,   In automotive MEMs gyroscopes are very common in navigation systems.  

    Sometimes not included in nano-technology or MEMs, but there are a lot of advances in developing sensors that can be built with CMOS or other chip-building technologies.  I'm aware there are some dissolved gas sensors that are completely solid state.  It is possible that technology like that, more interesting sensors useful for biomedical applications can be developed that are completely integrated to the supporting IC.

  22. James108
    September 24, 2013

    For a few prototypes, MPWs offer a good option.  However, we prefer a multi-layer maskset (MLM).  You get more prototypes but equally important you control the start of the wafers, you can hold wafers in the process to make simple changes like poly or metal up changes, and you control which options in the process will be used. Since you get significantly more devices, you can run ESD and latch-up and other qualification testing if desired. Therefore, with lower volume devices, you can even use the MLM maskset for initial production.  The cost for an MLM is more than a MPW but much much less than a full maskset. 

  23. James108
    September 24, 2013

    The solid state batteries (SSB) are rechargable.  Most of the implantables that we have been involved with can go through a periodic recharge.  Depending on the particular use case, the device might be recharged daily or weekly. Therefore the SSB can be a good option.  Of course a daily or weekly disposable devices can also leverage the SSB. 

    With respect to energy harvesting, the IEEE Solid State Circuit Conference in 2011 focused on medical devices.  There were a significant number of papers focused on low power and energy harvesting.  My general take-away from one of the papers that discussed various methods of energy harvest was the following.  With rare exception (RF harvesting) the ability to harvest and store any real useful amount of energy was extremely challenging. The focus in this case was toward body worn devices so a small form factor was important.

  24. jkvasan
    September 28, 2013

    James,

    Many biomedical engineers work in hospitals as maintenance engineers. As to product/device design, most of the engineers are from the electronics or electrical background. Only those BMEs who have done masters and above come into the design, research industry. I have seen very bright BMEs doing wonderful software work and design hardware well.

  25. SunitaT
    September 30, 2013

    Integrated circuits are established for sensor apps in medical transplants or other bio-electronics expedients. Specific sealing approaches have been taken in such biogenic surroundings to avoid erosion or bio deprivation of the open semiconductor resources. As one of the a small number of ingredients well recognized in CMOS tech, titanium nitride driven out as extremely steady and well suitable for electrode apps in medicinal implants.

  26. Brad_Albing
    September 30, 2013

    @fasmicro – I expect you will see more engineers apecializing in biomedical degrees. That is for sure where the money is now.

  27. Brad_Albing
    September 30, 2013

    @eafpres – here is a little more info on the topic:

    Batteries Can Be Printed Using 3D Technology

     

  28. Brad_Albing
    September 30, 2013

    @fasmicro – Of course, if they are bedridden, then an external power source – e.g., an inductive power coupling system – is more practical.

  29. fasmicro
    September 30, 2013

    The point is that anything that depends on mobility of the patient to power the implantable device may not be optimal. It is very different from tapping from the energy of an athlete to power his pedometer because the athlete is active. These guys are bedridden with limited mobility.

  30. fasmicro
    September 30, 2013

    >> I expect you will see more engineers apecializing in biomedical degrees. That is for sure where the money is now.

    Absolutely, it is already a very lucrative area and field. As the baby boomers retire and need more care, biomedical engineers will have great boom.

  31. yalanand
    November 30, 2013

    @James, Compared to the traditional lithium-ion batteries are these solid state batteries having any other advantages other than space. Is it cost effective to manufacture these solid state batteries ?

  32. James108
    November 30, 2013

    The SSBs are processed similarly to other integrated circuits using similar wafer manufacturing processes and tools.  In mass production, these devices are very cost effective.  However, at least for now the driving factor for choosing a SSB is usually space savings.  This may change if SSB capacity increases.

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