The Enabling Chip Technologies Behind Miniature Implantable Medical Devices

[Editor’s note: Co-authors are from Cactus Semiconductor Inc. — Andy Kelly, System and IC Architect, and James McDonald, President.]

Implantable medical devices (IMDs) have an approximate size of ~15 to 50 cc. Such devices are common for use in the chest or abdomen. They can be implanted there using long leads or catheters. IMDs often require invasive surgery to implant. Such IMDs include pacemakers, defibrillators, spinal cord stimulators, drug infusion pumps, and more. These devices are widely popular. However, today miniature implantable medical devices (MIMDs) are capturing much more attention as they continue to usher in a new era of treatment capabilities. The enabling chip technologies behind MIMDs will be critical to their continued adoption.

Today’s MIMDs consist of <4 cc volumes and are applied to areas of the body that include the head, neck, and limbs. They can often be implanted with minimally invasive surgery and sometimes even without surgery at all. A common non-surgical implant method is to use small leads or catheters. MIMDs include ECG/EEG monitors, peripheral nerve stimulators, micro infusion pumps, and other similar devices. A more specific example of an MIMD would be a nerve stimulator with a volume of <1 cc. This device would be small enough to implant at the point of therapy with minimally invasive surgery. With its small footprint compared to an IMD, it would not need to be implanted in the chest nor require long leads routed to the neck. Naturally, there are a lot of miniaturization technologies necessary to make it all happen. So, what are some of these MIMD enabling technologies?

Enabling technologies
Chip-scale packaging (CSP) is critical. The use of DIP, SOIC, and QFP packaging common with IMDs is replaced by QFN or WLP packaging in MIMDs. As a comparison, these new packages are 250 times smaller than, for example, a DIP package. In addition, stacked chip-scale packaging (SCSP) allows for multiple chips in one package. It’s possible to have stacked on a substrate an application-specific IC (ASIC), radio frequency IC (RFIC), microcontroller IC (MCU), and non-volatile memory (NVM) IC. This can provide complete system functionality in a single package. Packaging advances will continue to play a key role in enabling more and more MIMD applications.

Of course power capabilities are essential, too. With MIMDs, solid-state batteries (SSBs) are critical and have compelling key characteristics for their adoption. They are fabricated on silicon wafers with standard semiconductor processes and equipment. So there’s no big retooling required at any level. They also function much like rechargeable lithium-ion batteries but at a fraction of the size. These commonalities are important to keep design risks and cost low. As SSB capacities (uA-h) increase, application options for these batteries will continue to rise.

Micro-electromechanical systems (MEMS) are also key enablers. They include microscopic sensors, actuators, and machines manufactured with IC processes. Some examples include: pressure sensors for blood pressure and respiration, accelerometers for tracking position and activity, chemical sensors to track such things as glucose or pH, and fluid pumps for drug delivery. The features brought by MEMS are essential to many key MIMD applications.

Last but not least, ASIC chips provide very important features and capabilities. It’s easily arguable that most MIMD applications might be unattainable without the use of an ASIC. With a properly designed ASIC, one can eliminate unnecessary features and functions that wouldn’t be possible with off-the-shelf ICs. ASICs allow the best opportunity for optimization of performance for single applications. For example, ASICs allow best-in-class optimization of size and power for MEMS interfaces. Total power consumption is also best optimized using an ASIC. These optimizations can easily lead to reduced battery sizes and even enable the use of solid state batteries previously discussed. The synergistic impact of these enabling technologies are obviously important when developing an MIMD.

One research firm recently had the IMD market pegged at just a bit more than $43 billion in 2011 and reports it will grow to nearly $74 billion by 2018. And this is just the US market. As a component of this market, MIMDs are poised for more adoption. They are achievable by capitalizing on enabling technologies that provide design opportunities that address specific application needs. The companies that can leverage technology enablers to such an end will stand apart as clear successes.

15 comments on “The Enabling Chip Technologies Behind Miniature Implantable Medical Devices

  1. Davidled
    October 15, 2014

    Customer might request the testing report in terms of temperature and durability. It is believed that IMDs might be embedded inside body permanently. If IMDs get misbehavior against the body, the body could be infected by the tiny bit chip virus. Some patient might get the side effects from electronic chip. More clinic testing might be required before the product is released in the market.

  2. bjcoppa
    October 17, 2014

    IMDs typically have slower and more steady growth cycles than consumer electronics. The companies producing these devices do better during recessions than advanced microelectronics with volatile growth cycles. The industry benefits from using depreciated older generation tech and equipment as well.

  3. bjcoppa
    October 17, 2014

    Most of the medical device electronics have stricter standards to reach FDA approval over looser consumer electronics regulations. Node sizes are much less than for advanced electronics like mobile devices and they cannot benefit solely on common foundries as is often the case for many semiconductor fabless companies.

  4. fasmicro
    October 19, 2014

    Biasing transistors in the weak inversion or sub-threshold where the transistors fire up before it reaches the threshold voltage is also a very popular design paradigm in this sector. Many engineers have morphed the designs models used in small electronics watches into IMD. Subthrehold physics is one of those ways of doing same.

  5. amrutah
    October 19, 2014

    “Customer might request the testing report in terms of temperature and durability.”

    @DaeJ: As I understand the problem with w.r.t. to temperature is not a big concern, since the human body temperature remains in a very small temperature range (34degC-43degC).  The reliability, FIT rate is a one important aspect of biomedical chipsets.

  6. amrutah
    October 19, 2014

    “…solid-state batteries (SSBs) are critical and have compelling key characteristics for their adoption.”

    @James: Thanks for the information about the IMDs.

      What are these SSB are they something similar to carbon nanotubes?  Somewhere in 2013 there was a paper on the carbon nanotubes used for powering and building and growing the Heart muscles.

  7. amrutah
    October 19, 2014

    There are a few things that I really don't understand

    1> Say the device is reliable for 10 years, how is the problem tackled when it comes to its End-of-Life.  What is the stand by option for the patient using the implated device if the device suddenly stops.

    2> With people carrying so many electronic gadgets the EMI emissions pose a great threat (false triggers or failures) for these low voltage IMD devices.  These have to be systematically tackled.

  8. amrutah
    October 19, 2014

    @fasmicro: Yes, I agree.  A lot of medical IC designs are concentrating on biasing the enhancement MOSFET in weak inversion instead of using the BJT's.  One more great advantage is low voltage operation.  The only problem with weak inversion devices is less of dynamic range.

      The point of sub-threshold physics that you mentioned arises a question.  Does the standard berkeley spice model for devices good enough or do we have to use the EKV models, which are said to be good when it comes to sub-threshold mode of operation.

  9. ue2014
    October 23, 2014

    Totally agree with you. Since we are dealing with Human Health, we need to be extra careful about the dependability of our products. Therefore, many Human Testing would needed to make sure that these MMIDs does not have any side effects on human body and does not influence the natural behaviors. On the other hand, there should be a mechanism to check the situation of the MMID as well once it's inserted to the Human Body just to makes sure it's condition as well.

  10. bjcoppa
    October 24, 2014

    Radiation scanner companies are developing screening systems for airport security to check for implantable explosives within humans carrying out suicide missions. Typically an electromagnetic energy source reflects off the non-standard biological object implanted which generates an ultrasonic signal that is detected leading to alarm notification.

  11. James108
    October 24, 2014

    The solid state batteries (SSBs) are developed on silicon wafers much like ICs.  In fact, in some cases you can integrate the battery and the IC on one piece of silicon.  Although this currently is not the typical use case.  The SSB are rechargeable as well.

  12. vasanjk
    October 25, 2014

    Hi James Very interesting information. As I am from Medical device field, I am curious to understand how circuit protection is deployed in MIMDs as the focus is on miniaturization and low power consumption. In a typical electronic device, even a finger touch could create heavy ESD and we use Varistors and TVS diodes. My specific question is, do your chips incorporate such circuit protection devices internally?

  13. James108
    October 25, 2014

    We do include ESD protection on all of our pins.  The protection is to provide a minimum of 2000V HBM (Human Body Model).  We also do ESD testing with machine model (MM) and charge device model (CDM).  However, many user of our circuits, medical device companies, also include external protection schemes particular to address defibrillation events.

  14. vasanjk
    October 25, 2014

    Defibrillation events and electrosurgical generator interference can impact such applications. Good to know protection upto 2KV is available. Rest can be taken care of by dedicated circuit protection devices.

  15. ue2014
    October 27, 2014

    That's a great news. If this projects goes through, it would help the countries security as well as it could save many Human lives. Even such technologies would be used to serve many other purposes as well….

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