Power Management from Smartphones to Data Centers

Power has become a first-class design constraint in computing platforms from the smartphone in your pocket to warehouse-scale computers in the cloud.  Historically, semiconductor innovation has repeatedly provided more transistors (Moore’s Law) for roughly constant power per chip by scaling down supply voltage each generation.  Unfortunately voltage scaling has ended due to stability limits and chip power densities are increasing each generation on a trajectory that outstrips improvements in the ability to dissipate heat.

Earth Abundant Element Solar Cells from Nanocrystal-Inks and Molecular-Inks

Given the terawatt scale of future energy needs, the most promising future photovoltaic materials should be Earth abundant with their primary mineral resources distributed across several geographic regions and their supply chains robust to reduce concerns of price volatility. In addition, the process of forming the solar cell should be scalable, low-cost, and not utilize dangerous or toxic materials. The strongest initial candidate appears to be kesterite structures of Cu2ZnSnS4 (CZTS) and similar materials.

Energy from water: Microbial Fuel Cell Technologies Meet Salinity Gradient Energy

The ability of certain microorganisms to transfer electrons outside the cell has created opportunities for new types of energy generation including: microbial fuel cells (MFCs), to produce electrical power; microbial electrolysis cells (MECs), to produce fuels such as hydrogen and methane gases; microbial desalination cells (MDCs) to partially or fully desalinate water; and microbial reverse electrodialysis cells (MRCs) that can additionally be used to obtain salinity gradient energy. In an MFC, exoelectrogens oxidize organic matter and release electrons to the anode.

Energy-Efficient Photonics: Computing Applications and Fundamental Limits

Academic papers have routinely reported power per bit numbers in the low pJs for several years.  It may be reasonable to assume as an upper limit that deployed systems may achieve the one to two orders of magnitude improvement to reach 0.5 pJ/bit within the next 5 years.  These optimistic electrical link estimates still fall short of energy performance required by advanced microprocessors.  Here we demonstrate that the current state of photonic devices integrated in foundry CMOS foundry processes are competitive with existing and next generation on-chip power dissipation numb

Ultrafast Coherent Optical Signal Processing using Stabilized Optical Frequency Combs from Mode-locked Semiconductor Diode Lasers

The development of high speed communications, interconnects and signal processing are critical for an information based economy. Lightwave technologies offer the promise of high bandwidth connectivity from component development that is manufacturable, cost effective, and electrically efficient. The concept of optical frequency/wavelength division multiplexing has revolutionized methods of optical communications, however the development of optical systems using 100’s of wavelengths present challenges for network planners.

Nanostructured Energy Devices: Phonons, Electrons and Photons on the Nanoscale

Supplying the world with sustainable energy is one of the most pressing issues in modern society. Dramatically improved control over heat, electricity and solar energy is essential to create a new energy paradigm. Nanomaterials with carefully tailored properties (such as interface, geometry) can be used to manipulate the flow of phonons, electrons and photons, to enable novel energy devices in an unconventional manner. In this talk, I will present three examples of nanostructure-enabled energy devices.

Interfacial Charge Transfer in Nanomaterial Based Light Harvesting Devices

We purposefully design and study “molecular-like” interfacial interactions between the multidimensional nanometer-scale building blocks that compose larger-scale functional light harvesting devices. Using time-resolved optical spectroscopy, we aim to understand the nature of discrete interfacial electronic states and their role as crucial intermediates promoting efficient interactions between extended systems (e.g., charge transfer).

Using Asymmetric Crystals for New Functionality: Moving Spins with Heat Using Spin-Orbit Coupling and Dopant-less Diodes Using Polarization Charge

The lack of inversion symmetry in certain crystals leads to interesting properties. Two such properties, the spin-orbit effect and polarization charge, can be exploited for new thermoelectric and optoelectronic devices. In the first part of the talk, I will introduce the heat/spin conversion phenomenon, the spin-Seebeck effect. Phonons interact with the magnetic moments in a material driving them away from equilibrium inducing a diffusive spin current, which can be converted in a neighboring material into an electric voltage.