Probably the number one most interesting thing I saw at the PCIM show in Nuremberg, Germany last week wasn’t an IGBT, or even a MOSFET. It was a battery.
I had the chance to meet with Steve Grady, VP Marketing at Cymbet. Cymbet has developed a solid state battery which is intended to replace coin cell batteries and supercapacitors in certain applications. These incumbent technologies use toxic materials and are therefore difficult to dispose of. They are also relatively bulky. Cymbet’s solid state battery, EnerChip, is a small semiconductor die that does the same job, except it’s non-toxic. It can be supplied as a semiconductor die for incorporation into packaging alongside other die, or it comes in a reflow solderable IC package along with some power management electronics. The batteries can then be handled just like any other IC on the production line.
Packaged products range from a 5uAh (2.5mAh lifetime) battery in a 4x5mm DFN up to a 50uAh (25mAh lifetime) battery in an 8x8mm QFN package. There are various bare die options as well. Solid state batteries lose only 1-2% of their charge per year when not used (supercaps lose 10-20% per day, by comparison). They are rated for 3.3 or 3.8V.
These devices are being used as backup batteries for things like real-time clocks (RTCs), in case the system is disconnected from the main battery. They are also good for powering tamper-detection circuits. Here comes the even more interesting part. EnerChip has been passed as 100% biocompatible by in-vivo tests, meaning it is safe for use in implantable medical devices.
One of the most compelling biomedical applications Grady showed me was a tiny pressure sensor that can be implanted into the eye of a Glaucoma sufferer. Since patients with Glaucoma can deteriorate within a matter of hours, a sensor that measures the intraocular pressure continuously would be very valuable in monitoring this condition. An EnerChip die was used in the same custom package as the tiny sensor system it powers, which is embedded in the patient’s eye. EnerChip, used in this configuration, can be recharged using RF induction and can withstand more than 5000 charge cycles. In this particular application, the time between charges was about 28 days.
Grady also spoke about incorporating the same technology, in the form of a special crescent-shaped die, onto a contact lens to power electronics in the lens, like a head-up display. Perhaps we’ll be seeing this technology in a future version of Google Glass!