Masakazu Shoji

Analysis of high-frequency thermal noise of enhancement mode MOS field-effect transistors

The high-frequency thermal noise in the drain and the gate of an enhancement mode MOS field-effect transistor was analyzed by using the transmission line model of the channel. The analysis gave the mean squared noise current generators of the drain and the gate and their correlation. The correlation coefficient of the drain and the gate noise was zero for zero drain voltage and was 0.395j at saturation. The noise figure of the MOS field-effect transistor was calculated from the result of the analysis. The high-frequency noise characteristics of an MOS field-effect transistor were similar to those of a junction gate field-effect transistor.

Functional bulk semiconductor oscillators

This paper describes the generation of various waveforms with bulk semiconductor (Gunn-effect) oscillators having non-uniform cross sections or connected to external resistive circuits by means of small contacts attached to the bulk between the cathode and anode. In nonuniform oscillators, if the variation of the cross section is gradual, a high-field domain is equivalent to a constant current density generator moving at constant velocity. From this simple model, oscillating current waveforms are closely related to the cross-sectional area of the device. The oscillating frequency can be tuned or switched by the bias voltage. In multiterminal oscillators, the cathode current changes whenever a domain passes one of the small contacts connected to the external circuit. The waveforms can be controlled by changing the external circuit parameters. The characteristics of these devices operating in the frequency range from 50 to 150 MHz were extensively studied by changing both the device configuration and the external resistances.

Theory of Transverse Extension of Gunn Domains

A theory describing the growth of Gunn domains transverse to their direction of travel is developed. This theory is based on a model in which the dipole moment of a domain causes the field immediately adjacent to its lateral edge to exceed the negative resistance threshold. As the dipole moment begins to build up there, it causes the field farther along the lateral dimension to exceed threshold. From this model the velocity of transverse domain growth can be calculated as a function of the bias field and the maximum domain field. The calculated values of about 108 cm·sec−1 are in reasonable agreement with available experimental data.

Two-dimensional Gunn-domain dynamics

In two-dimensional bulk GaAs devices, each small segment of a high-field domain can be considered to move normal to its front, with a velocity equal to that of a one-dimensional domain having the same domain potential. Using this simple model, an equation describing the domain shape in two-dimensional samples was obtained. When edge nucleation effects are taken into account, the solution of the equation provides a good explanation for most of the domain motions observed experimentally in various samples of non-uniform shape. The experimental observations were made using a resistive probe. The probe experiments enable one to visualize how domains behave in devices with sudden or gradual changes in width, with sharp or gradual bends, and with multiple terminals. In an Appendix, the simple model of two-dimensional domains is justified using a perturbation theory.

Bubble forces in cylindrical magnetic domain systems

The force exerted on a bubble by a current and by other bubbles is calculated. We examine the force on a bubble from straight current‐carrying conductors of finite width and length and from conductors that are bent. We find that if the conductors width is less than or equal to a bubble radius, the force on a bubble from a conductor pattern may be approximated by zero‐width connected current‐carrying segments. The mutal repulsive force between two bubbles is also determined. An important feature of this calculation is that the mutual decrease in bubble radii that occurs as two bubbles approach one another is taken into account. Bubble‐bubble force curves as a function of material thickness are given for bubble spacings corresponding to typical current and field access circuits.

Focusing of a Light Beam by a Concave Magnetic Domain Wall in Yttrium Orthoferrites

We have observed the convergence of a light beam that has passed through a concave boundary of magnetic domains in orthoferrites. We have developed a simple theory that explains the phenomenon.

Small-signal impedance of bulk semiconductor amplifier having a nonuniform doping profile

A convenient method for studying the small-signal impedance of a bulk semiconductor amplifier having a nonuniform doping profile is presented. The small-signal impedance is represented as a two-dimensional sum of the interaction impedance which represents the electrical interaction between various sections in the amplifier due to the transport effect. When the diffusion current is negligible, the two-dimensional plot of the magnitude of the interaction impedance shows which part of it is important. The two-dimensional representation may provide a convenient method of synthesizing the doping profile of a bulk semiconductor amplifier which gives a desired impedance characteristic.

COMMENTS ON ``LOW‐FREQUENCY CURRENT FLUCTUATIONS IN A GaAs GUNN DIODE''

Our measurements of the small signal conductance of a GaAs Gunn diode at low field values do not show the frequency dependence reported by K. Matsuno.

Quantum Mechanics of Digital Excitation

The characteristics of the cascaded digital gates in a large-scale chain or mesh structure, where the switching transients develop by traveling signal fronts, are examined in Chapter 1. In this chapter, I proceed to study the characteristics of the transients created in the gate-field, which I call excitation. The most fundamental attribute of an excitation is that it is an undividable whole and has its own identification. Particles and waves in three-dimensional physical space are examples of excitation. An excitation carries energy, information, and, often, mass. Thus, digital signals propagating in a logic-gate chain are excitations created in the gate-field. The nature of an excitation reflects the background properties of the field. Since I stressed the similarities between physical space and the gate-field in Chapter 1, here I begin by pointing out the differences between the two. The differences are crucial to an understanding of digital excitation in digital circuits. There are four fundamental differences between physical space and the digital gate-field, which reflect back to the excitations they support: (1) The physical space is continuous with respect to any of the three spatial coordinates, down to the presently accessible limit, but the digital-gate field is discrete, having the integer node-location index. (2) A point in physical space exercises a noninverting influence on its neighbor point, but the digital-gate field may exercise either inverting or noninverting influence on its immediate neighbor, depending on the structure of the individual point of the gate-field. This is an important resource for adding variety and flexibility to the gate-field model. (3) Physical space appears to allow an infinitely large dynamic range of field variables, but the digital-gate field allows only a limited dynamic range of the gate-field variables. The gate-field has a power supply as the energy source that does not allow the voltage variable to exceed the range set by it. Certain field variable values are asymptotic values: An idealized excitation in a finite range may extend over the entire range of the gate-location index, and as the gate location index tends to plus or minus infinity, the field variable takes the asymptotic values at the infinities. (4) An excitation in a physical space moves in any direction of physical space, but a digital excitation in a conventional structure moves only in one direction. To make it bidirectional, a certain structure and definition are required (see Section 1.03).

Propagation of Digital Excitation in the Gate Field

Many compelling similarities among mechanical phenomena, including quantum-mechanical phenomena and digital-circuit transients provide motivation to initiate a research project to examine whether or not there is any deep-level connection among them. The theory of relativity showed that mass is a form of energy. Why, then, can a digital excitation that carries energy not be considered to be a mass point? Yet such a study would only serve to satisfy pure academic curiosity, if that were its only rationale. There are other incentives to go forward with such a study. Since its introduction, the quantum world has remained a fantasy world, accessible only to those armed with logical reasoning and advanced mathematics. The connection between the digital circuit and quantum mechanics provides a new viewpoint. Since the advent of the microprocessor, digital circuits are everywhere. As a model of the quantum world, they can help make the mystery world more accessible. At this point, a basic question must be asked: is the quantum world really unusual or exotic, or it is just a part of nature that happened to escape our attention until recent years due to a lack of familiar examples? I am inclined to believe that the quantum world is really a part of tangible nature and that it can have many varieties. The function of the human mind has been attributed by several influential authors to quantum-mechanical phenomena (Stapp, 1993; Penrose, 1994). Yet the neuronic systems are more concretely described as a special digital circuit than as a quantum-mechanical object. What then are the functional connections between the two?