William A. Stapleton

Applications of CCTO supercapacitor in energy storage and electronics

Since the discovery of colossal dielectric constant in CCTO supercapacitor in 2000, development of its practical application to energy storage has been of great interest. In spite of intensive efforts, there has been thus far, no report of proven application. The object of this research is to understand the reason for this lack of success and to find ways to overcome this limitation. Reported herein is the synthesis of our research in ceramic processing of this material and its characterization, particularly with the objective of identifying potential applications. Experimental results have shown that CCTOs permittivity and loss tangent, the two most essential dielectric parameters of fundamental importance for the efficiency of a capacitor device, are intrinsically coupled. They increase or decrease in tandem. Therefore, efforts to simultaneously retain the high permittivity while minimizing the loss tangent of CCTO might not succeed unless an entirely non-typical approach is taken for processing this m...

A novel engineering outreach to high school education

The demand for Science, Technology, Engineering, and Mathematics (STEM) students consistently outpaces supply. One of the recognized means for improving the readiness of high school students for STEM-related careers is outreach to high school programs. The newly created Ingram School of Engineering at Texas State University - San Marcos has partnered with the E3 Alliance and Project Lead The Way (PLTW) to create an opportunity for high school students to receive college credit in engineering disciplines for a set of advanced high school STEM courses.

Magnetically tuned varistor-transistor hybrid device

The paper deals with the effect of magnetic fields on the I-V characteristics of an IHC45 varistor. It is found that: (a) the nonlinear I-V characteristics of the varistor can be tuned by a magnetic field resulting in enhanced device performance; and (b) the contributions of a magnetic field on the output signal show all the characteristics of a typical transistor. The potential applications of these devices could be magnetically controlled voltage amplifiers, magnetically controlled current amplifiers, sensors, memory elements, microphone pickup with integrated pre-amplifier using a single transistor, and high temperature electronics.

Properties and Applications of Varistor–Transistor Hybrid Devices

The nonlinear current–voltage characteristics of a varistor device are modified with the help of external agents, resulting in tuned varistor–transistor hybrid devices with multiple applications. The substrate used to produce these hybrid devices belongs to the modified iron titanate family with chemical formula 0.55FeTiO3·0.45Fe2O3 (IHC45), which is a prominent member of the ilmenite–hematite solid-solution series. It is a wide-bandgap magnetic oxide semiconductor. Electrical resistivity and Seebeck coefficient measurements from room temperature to about 700°C confirm that it retains its p-type nature for the entire temperature range. The direct-current (DC) and alternating-current (AC) properties of these hybrid devices are discussed and their applications identified. It is shown here that such varistor embedded ceramic transistors with many interesting properties and applications can be mass produced using incredibly simple structures. The tuned varistors by themselves can be used for current amplification and band-pass filters. The transistors on the other hand could be used to produce sensors, voltage-controlled current sources, current-controlled voltage sources, signal amplifiers, and low-band-pass filters. We believe that these devices could be suitable for a number of applications in consumer and defense electronics, high-temperature and space electronics, bioelectronics, and possibly also for electronics specific to handheld devices.

Nature and Characteristics of a Voltage-Biased Varistor and its Embedded Transistor

An unorthodox approach for producing simple and yet practical transistors based on ceramic platforms is discussed in this paper. To achieve this, we modify the original nonlinear current-voltage (I-V) characteristics of a varistor by superimposing a biasing voltage (Vb). This leads to the formation of a hybrid device consisting of a biased varistor and transistor. The studies were done under two experimental conditions; first, when the ratio between the drain current (Id) and the bias current (Ib) is of the order of 103 or more, and second when it is less than 102. The transistors embedded in the hybrid device exhibit the typical attributes of a conventional transistor. The transistors are analogous to the well-established bipolar junction transistors and yet different because they are based on different physical principles. These transistors can meet the requirements of many general purpose applications and can also function satisfactorily as low-pass filters. The specialized applications could be under hazardous conditions such as at high temperatures, in radiation-filled environments such as outer space, and possibly in bio systems. The biased varistor assumes the property of mutual conductance like a transistor as well as becomes a good signal amplifier.

Magnetically Tuned Varistor and Its Embedded Transistors

This paper describes the properties and potential applications of a hybrid device consisting of a varistor diode and its embedded transistor whose origin lies in a magnetically tuned varistor diode. It is shown how the output current (or voltage) of a varistor based on a magnetic oxide semiconductor can be manipulated by the application of a magnetic field to produce an embedded device with characteristics similar to that of a conventional transistor. Following the tradition of microelectronics, we name it the HFET transistor where H stands for a magnetic field. Two types of embedded HFET devices are described here; one with the current-voltage (I-V) characteristics and the other with voltage-current (V-I) characteristics. Both I-V and V-I devices exhibit high degree of nonlinearly but only in the V-I mode of the HFET device well-developed saturation regions of output signals are found. The room temperature HFET in its V-I mode appears to be also a good electronic switch with well-defined “off” and “on” states. Saturated regions of output signals and electronic switching are the signature property of these HFET transistors along with the capacity of providing a good level of signal amplification. When cooled to 100 K the HFET V-I device appears to lose partially the electronic switching property but gain in signal amplifying potential. The HFET device in I-V mode does not display the defining properties of electronic switching but can amplify signals by almost 400%.