1. What’s an Evercell™?
Evercell™ power cells by Evergreen® Technologies, LLC – one of The Face® Companies – are passive-structure, semiconductor-based thermal energy harvesters that produce a small, continuous flow of electric power in virtually any environment where the temperature is above absolute zero. They will therefore eliminate the need for batteries in a broad array of low-power sensors, embedded circuits and wireless communicating devices. These patented and patents-pending power cells consume no fuel, have no moving parts, contain no toxic materials, and require no exposure to other external stimuli, including motion, pressure, RF or electromagnetic energy.
2. How does Evercell™ work? What’s the energy harvesting mechanism?
The Evercell™ harvests thermal energy in environments with no perceptible thermal differential. Each component or constituent element has a passive four-layer structure made of specially engineered materials. Opposing electrodes, one being surface treated to lower the work function of its facing surface, are placed in close proximity, sandwiching a dielectric layer with a thickness of 200nm or less. Based on the design difference in work function of the opposing electrode surfaces, electrons migrate away from the surface of one of the electrodes and accumulate near the surface of the other electrode, thereby establishing an electrical potential in the cell.
3. What do you mean by “work function” here?
Work function is the energy, usually specified in electron volts (eV), that is needed for an electron to leave a surface of a material. In solid-state physics, the work function is the minimum thermodynamic work (i.e., energy) needed to remove an electron from a solid to a final electron position remote from the surface on the atomic scale. The work function is not a characteristic of the bulk material but rather a property of the surface of the material.
4. Are there other structural factors that are important to Evercell™’s operation?
The proximity (<200nm) of the opposing conductor surface is critical, because it promotes quantum tunneling of the electrons from the electrode surface with the lower work function surface to the surface of the opposing electrode with the higher work function.
5. What is the potential electrical power out of an Evercell™?
At this early stage, we’re unsure what the upper limit may be. Individual Evercell™ modules can be connected in series and in parallel, as necessary. Here are some examples of expected performance for first-generation production devices:
• 5 μW device: 34mm x 34mm x 1mm — 1.2V output, 4.2 μA continuous current
• 960 nW device: 50mm x 75mm x 0.1mm — 1.2V output, 800 nA continuous current
• 480 nW device: 30mm x 305 mm x 0.2mm — 1.2V output, 400 nA continuous current
6. Can Evercell™ really be used as a battery substitute?
Yes, with an appropriate interface circuit, there are many applications where Evercell™ will be the preferable alternative to batteries, such as powering wireless sensors and communications nodes in the Internet of Things. Up to now, based on the assumption that there’s no substitute for battery power for most wireless devices, the focus of research and innovation has been to reduce the device’s power requirements, thus extending the life of the battery. Ironically, this steady reduction of power need has opened the way for Evercell™ and the elimination of batteries in billions of cases.
7. How big an impact could this have on the Internet of Things?
In the fall of 2017, before the invention of Evercell™ was publicly revealed, the world’s leading analysts of the IoT’s potential for growth and proliferation were reported by IDTechX to have estimated that the potential population of IoT devices would be five times larger if a viable substitute for batteries could be identified. As Evercell™ becomes available, it will open the possibility of embedding wireless sensors within the concrete of bridges and dams, or placing them in remote or hostile environments where the cost of changing batteries would be acceptably high, or implanting them in patients to power medical devices.
8. Medical devices?
Yes, although deployment could take a while because of the government approval process, the potential medical applications of Evercell™ are extraordinary. Since Evercell™ can provide a non-chemical, non-toxic, bio-neutral source of power that won’t run down, one can easily foresee its use within the human body, driving monitor or stimulator devices. Compare this, for example, with a conventional heart pacemaker, where surgery is required to change the battery.
9. How is Evercell™ fabricated?
To make an individual Evercell™ element, a first conductor layer for the donor surface is formed on a substrate. The donor surface of the conductor layer is conditioned to reduce its work function to be in a range of 1.0 eV or less. A dielectric layer, with a thickness in a range of 200nm or less, is deposited on the first conductor layer using any one of a number of conventional layer deposition methods. A second conductor layer formed of a material to present a facing surface with a work function in a range of typically 2.0 eV or greater is then formed on the dielectric layer.
Layered elements formed in this way may then be stacked, with insulating layers interposed between them, and may be interconnected in series or in parallel as needed to meet voltage and current-out requirements. Each of the individual layered elements may be multiples of tens of nanometers thick, and may be sandwiched between insulating layers, each of which may be on the order of 10 µm thick. The resulting Evercell™ device, including a stack of 50+ insulator-separated layered elements surrounded ultimately by an outer insulating shell, may have a total thickness in a range of 50 mils or less. So, for example, integrated circuit elements could be configured to be individually self-powered.
10. It must be expensive to make.
No, Evercell™ is made from readily available materials, and existing semiconductor production lines can be readily retooled to produce it. Once mass production is achieved, cost per unit is likely to be somewhere in the range of the battery being replaced.
11. Are there any toxic materials?
No, Evercell™ manufacture involves no toxic materials, and its production of energy is not dependent on any chemical reaction. So, unlike the conventional battery, Evercell™ is environmentally safe to make and operate, and to dispose of at the end of the service life of the sensor or other device that it powers. This, along with the elimination of the requirement for routine replacement, makes Evercell™ a very attractive battery substitute and expands the range of deployment options well beyond what’s achievable with battery power.
12. How’s your patent protection?
Very good. We have three issued U.S. patents for this technology, six additional patents to issue within months, and more pending in the U.S. and internationally. Our patent counsel is ensuring that we have overlapping coverage for every aspect of the technology and for a number of identified “use cases.”
13. So, can you recap the advantages of Evercell™?
· Evercell™ enables small wireless sensors and controls in the IoT and elsewhere to operate without batteries for the life of the device.
· It provides continuous output without a perceptible temperature differential (in essentially any environment above absolute zero).
· Its structure is solid-state.
· Its output is scalable and it can be made in various form-factors.
· It relies on no toxic materials in its production or operation, and can therefore reduce the environmental hazards presented now by batteries.
· It will be inexpensive to manufacture once mass-production is established.
· It leverages existing semiconductor manufacturing processes.
· It will enable the design of self-powered integrated circuits for the IoT.