We recently made a press release regarding the micro supercapacitors that you wrote a scientific article about. Now you’ve had another publication about this. What is it that you’ve done this time, and how does it connect with your earlier publication and work?
"So, previously we had demonstrated fabrication of micro energy storage units called Microsupercapacitors through “enhanced spin coating” methodology that can be implemented with integrated circuit (IC) fabrication using only one material such as graphene oxide, or vertically aligned carbon nanosheets, and carbon nanotubes. While, the spin coating method can demonstrate high coverage of material inks, increased uniformity and adhesion; these devices cannot exhibit high enough energy densities due to the layered thickness. In this article, we have shown that the microsupercapacitor performance can be improved by utilization up to four different materials, all layered through the same fabrication process i.e. spin coating.
These materials are composites of graphene oxide synthesized by Dr. Ulises Mendez, especially tailored for improved spin coating and incorporation of novel 2D materials that are presently being researched at various energy storage material centers. The device performance of the stack of electrodes results in a up to three times higher performance compared to our previous publication without completely overhauling a preset fabrication process. This publication leads us closed towards standardized IC compatible integration of Microsupercapacitors while incorporating various synergistic effects from latest energy storage materials developed at state of the art labs."
Your dissertation is April 29. Tell me about the topic of your work as a doctoral student, and why you wanted to focus on that in particular?
"The topic of my dissertation is “On-chip electrochemical capacitors and piezoelectric energy harvesters for self-powering sensor nodes”. In this work, we have demonstrated successful fabrication of Microsupercapacitors as on-chip solution for energy storage and silicon cantilevers based on two degree of freedom structures to validate a large bandwidth of frequencies that have the potential to harvest vibrational energy, also on-chip. In this work, I have mainly focused on understanding the requirements of an on-chip power supply that can be in some sense “ever-lasting” through ambient energy harvesting and high cyclic stability of Microsupercapacitors. A combination of these units with a power conditioning circuit can potentially replace, as a long term aim, and complement, in the short-term, batteries. We wanted to focus of replacing batteries, because, in-spite of being a better solution to fuels, the batteries cannot achieve high power densities that are required for short bursts of applications, eg, vehicles with hybrid powering technologies still cannot be used for transportation of heavy loads while driving up a slope. A supercapacitor with an energy harvesting source can act as complementary units with the energy storage system module that can provide such short power bursts."
What are the most important findings, would you say?
"The most important findings for my PhD can be described as follows:
Vibrational energy harvesting is an attractive solution for micro power harvesting from areas that are inaccessible to sunlight, heat, or human interaction. Their utility however is limited to the bandwidth of useable frequencies. In order to improve the bandwidth, application of two degree of freedom (2DOF) cutout cantilevers can be a potential solution. Advantages of improved bandwidth and relative feasibility of fabrication through IC processing make them a stand out solution among a myriad of other promising solutions. Another important finding for vibrational energy harvester concerns the gap between the design and fabrication constraints. It is extremely important to address trade-offs of designing and manufacturing.
Energy storage through batteries and supercapacitors is often a bottleneck for miniaturization of sensor nodes for wireless sensor networks. Thus, miniaturization to Microsupercapacitors is the next stage of evolution for on-chip energy solutions. While several promising materials have emerged through continuous research in nanomaterials, graphene as an energy storage material is close to integration with various IC technologies. Using graphene based inks deposited through conventional IC compatible methodology such as spin coating can be challenging due to its flake size and substrate roughness. Increasing the roughness of a substrate can improve the adhesion, coverage, and uniformity of the spin coated graphene ink, leading to an improved yield in the IC compatible device fabrication. The energy density of the Microsupercapacitors can be improved by stacking several materials spin coated on the same substrate using enhanced surface roughness technique without tweaking a standardized fabrication process."
What challenges have you been facing along the way?
"To name a few would be a dis-service to the ones I have forgotten. PhD students are expected to know how to do “everything” and the steep learning curve that is demanded for developing new advancements is often challenging. We can often forget the time that is required to learn, re-learn and sometime un-learn a skill. Another challenge that perhaps we all encountered was a once in a lifetime pandemic. I don’t think we have still recovered from the loss that we all suffered in that time. I think the challenges of a PhD student cannot be limited to just research. It is becoming more and more important to address issues of mental stress with PhD studies and demands of academia. We have come from various communities across the world with different dreams, aims, and aspirations to a country which every person in the world can be proud of. However, the immigration policy of Migrationsverket is often an a severe source of stress for us. Not only does it fill us with insecurity about the future, but it also acts as a barrier for many of us to be completely immersed in the beautiful surroundings and act in healthy and positive ways. I think it would be important to address these issues in collaboration with PhD students, faculty, institute, and policy makers in the future for a healthy and sustainable functioning to the technology cycle."What’s your plans for the future?
"As of now, I want to rest on the 30th after knowing what happens on 29th. Sunny weather will be welcome. Maybe a trip to Thailand. Otherwise, I plan to continue development of microsupercapacitors as viable energy storage units. I think such a device can be a solution to energy storage problem, we are facing right now. Otherwise, my focus would be on being in better health, spending more time with my loved ones, and working towards making our society better, more inclusive, and peaceful."
Text: Robert Karlsson
Photo: Agin Vyas