Devices that exhibit a phenomenon known as negative differential resistance (NDR) have tremendous potential to deliver the kind of low-power circuitry needed in a variety of electronics applications. To understand NDR, it is instructive to recall Ohm’s Law, V=IR. For a fixed resistance (R), as voltage (V) increases, current (I) increases in a linear fashion. In NDR, there is a voltage range where increasing voltage actually results in a decreasing current. This behavior has many beneficial design properties, one of which is the design of low power memory and logic or even energy scavenging from the environment, eliminating the need for a self-contained battery. Until now, successful demonstrations of NDR have been limited to rigid, inflexible semiconductor-based devices that are unsuitable for certain applications. Researchers at The Ohio State University have developed a polymer-based device that exhibits NDR and has the flexibility needed for advanced applications such as smartcards and wearable electronics. These devices enjoy very fast operation, which leads to high performance while consuming very little power. Furthermore, these devices can be manufactured in a very cost-effective manner using simple printing techniques.
Development of advanced logic and memory circuits on flexible substrates
Large and reproducible NDR, at room temperature, in a flexible polymer device!
There is great interest in developing new solid state semiconductor-based light emitting diodes (LEDs) that exhibit new functionality and performance. Principal challenges in creating new semiconductor LED structures include the formation of defects and low doping efficiency, both of which negatively affect device performance. To overcome these challenges, researchers at The Ohio State University have developed new methods and device structures that lead to defect-free, high-efficiency nanowire LEDs. These LEDs can be easily mass manufactured and integrated in silicon electronics, and can hit any bandgap due to the lack of strain relaxation.
Defect-free formation during epitaxial growth
Enables simple and broad bandgap engineering
Low manufacturing costs and easy integration into Si electronics
Passive imaging systems and radiometers require highly sensitive detectors that can operate at millimeter-wave frequencies. Biased Schottky diodes are commonly used for these applications, but the required biasing circuit greatly increases the system and pixel complexity and also leads to extra noise and drift. Zero-bias diode detectors are advantageous because no biasing circuit is required, but they require a large zero bias nonlinearity or curvature. Discrete Ge backward diodes and planar-doped barrier GaAs diodes have previously been used for zero bias detection with high nonlinearity. However, because of the chosen substrates, these devices are not readily suitable for imaging applications, where a mass-producible technology is required to fabricate a large number of identical devices into compact pixilated imaging arrays. Sb-based heterojunction backwards diodes are also excellent candidates for zero-bias detector applications due to their high sensitivity, high bandwidth, modest temperature dependence, and mass production capability. However, the high cost of Sb-based backward diodes and their incompatibly with mainstream Si read-out circuitry makes them undesirable for cost-sensitive applications and system-level integration. In order to alleviate these issues, researchers at The Ohio State University have co-developed a Si-based backward diode that is affordable, mass-producible, and can be readily integrated with standard CMOS circuitry. The devices exhibit large zero bias curvature and a low zero biased junction resistance, all at room temperature. The combination of outstanding device performance and compatibility with Si-based electronics makes these devices ideal for highly sensitive imaging and radiometry applications.
Passive imaging and radiometry systems
Screening and detection of concealed weapons
Vision enhancement for navigation through obscuring weather
High zero-biased curvature, resulting in outstanding sensitivity
Researchers at The Ohio State University have developed a comprehensive portfolio of Organic Light Emitting Diode (OLED) technologies that include novel materials and device architectures as platforms for functional devices and for device manufacturing. These developments improve material stability over time while improving their performance such that the required voltage can be reduced and improved electroluminescence can be obtained with reduced power consumption. The bilayer device structure improves device quantum efficiency and brightness due to charge confinement and exciplex emission at the emitting polymer interface. Beyond advancements in the materials themselves, novel device architectures have been developed which are independent of the materials used. These advancements may be of significant value in simplifying manufacturing, thereby accelerating the displacement of LCD and plasma display technologies as well as the displacement of traditional incandescent and fluorescent lighting sources. The associated patent portfolio consists of 8 patent families with a total of 11 issued U.S. patents and 39 associated national stage filings (spanning all US cases). A listing of all issued U.S. patents can be found below.
Conformal, designable, and color-variable interior and exterior lighting for residential and commercial environments
Power and weight sensitive lighting and display applications (e.g. aircraft interior lighting, portable display backlighting)
Portable lighting devices such as flashlights
Light, ultra-thin, flexible displays with rich colors viewable from very wide angles
Body-wearable lighting and display applications
Nearly endless list of potential applications
More energy efficient lighting source compared to incandescent and fluorescent approaches
Color quality matches or surpasses conventional approaches in lighting and display applications
Estimated useful life is approximately 17-25 times longer than incandescent lighting and nearly twice as long as linear flourescent lighting (which is commonly used in modern LCD displays)
Polymeric material is conformal to a wide range of surface topologies and allows for ultra-thin, flexible displays
Low cost, materials-independent architectures have the potential to lower manufacturing costs
Silicon-based field effect transistor (FET) devices are building blocks of silicon-based digital, analog, and hybrid electronics. Often made of a metal-oxide-silicon (MOS) type structure, these devices are interconnected to generate so-called "complementary" MOSFET circuits, known as CMOS transistor circuitry. CMOS enjoys the benefits of low power and high speed operation, and advancements in these two properties have primarily been achieved through reduction of the channel length, which is now well into the submicron range for commercial devices. However, CMOS technology is approaching certain fundamental limits that will prohibit further miniaturization, likely due to the complex material formulations used. To overcome these limits, researchers at The Ohio State University have developed a novel Tunneling Field Effect Transistor (TFET) that will allow for further device miniaturization, reduced power, and increased speed beyond what is possible with current CMOS technology, while still enabling the use of well-established CMOS manufacturing processes.
Power-constrained military systems
Practically anywhere silicon-based electronics are used
Extends CMOS, enabling a new generation of device topologies while allowing the use of current manufacturing processes
Faster turn-on at lower voltages than competing TFET designs
Steep sub-threshold slopes (below 60mV/decade)
Less current leakage in the "off" state compared to competing TFET designs
Higher current densities in the "on" state compared to competing TFET designs
Since the early 1960’s, the utility of the tunnel diode (or Esaki diode) has been evident, but several practical hurdles have kept it from reaching mainstream status. Historically, it has been difficult to control peak current and, more importantly, tunnel diode fabrication has lacked a Si-based process that can easily be mass produced and integrated into existing Si-based integrated circuits. As a result, today’s tunnel diodes are primarily used in discrete form and for niche applications. Regardless, tunnel diodes have many current and future applications, and the challenges of aggressively scaled CMOS is forcing this subject to be seriously revisited, since quantum tunneling will dominate in any ultra-low dimensional material. The structure of the Resonant Interband Tunneling Diode (RITD) differs from that of the Esaki diode (traditional tunnel diode) which results in additional useful properties. In RITDs, electrons quantum mechanically tunnel across an energy well formed between two barriers, where Esaki diodes have no energy well. This quantum mechanical tunneling effect happens extremely quickly and thus very high speed electronics can be realized with the use of RITDs. Terahertz operation has been demonstrated. Furthermore, a useful effect called Negative Differential Resistance (NDR) can be exploited using these devices.
Can augment CMOS technology resulting in novel logic and embedded circuit topologies with reduced device count, low power, and faster speed.
Can be implemented in ICs, memory devices, and small, lightweight portable electronics for greater performance at lower power consumption
Applications found in oscillators, frequency locking circuits, advanced SRAM circuits, highly integrated A/D converters, high speed digital latches, and many others
Uses quantum tunneling, a very high-speed process. Terahertz operation has been demonstrated
Shown to exhibit Negative Differential Resistance (NDR)
Low cost, compatible with current CMOS technology, and easy to integrate into existing manufacturing processes
Runs at room temperature and at very low voltage
Can be combined with existing technologies to offer flexibility
Tunneling Diode: Use and Manufacturing – US Pending Using Backward Tunneling Diode as a Sensor – US Pending