US3569895A

US3569895A - Inhomogeneous magnetoresistance devices

Info

Publication number: US3569895A
Application number: US833489A
Authority: US
Inventors: Hiroyuki Fujisada
Original assignee: Int Trade & Industry Japan
Current assignee: Int Trade & Industry Japan; International Trade & Industry Japan
Priority date: 1966-08-15
Filing date: 1969-06-16
Publication date: 1971-03-09
Anticipated expiration: 1988-03-09

Abstract

A solid state element having layer form inhomogeneities in impurity concentration is positioned within a magnetic field and experiences changes in resistance when subjected to energy in the form of a standing sound wave, a travelling sound wave, a change in direction of a magnetic field, or light in a pattern of alternating intensity.

Description

0 United States Patent 1 3,569,895

[72] Inventor Hiroyuki Fujisada [51] lnt.Cl H0lc 7/16 Tokyo,Japan [50] Field ol'Search 338/13, 14, [21] App]. No. 833,489 15, 17, 32, 32 (H) [22] Filed June 16, 1969 4s 1 Patented Mar. 9, 1971 [561 References CM [73] Assignee Agency of Industrial Science & Technology, UNITED STATES PATENTS Ministry of Internati nal Tra e & In u ry 2,894,234 7/1959 Weiss et a1 338/32 ymJ p 3,143,448 8/1964 Mette m1 338/32X [32] Priority Aug. 15,1966 3,286,161 11/1966 Jones et a1. 338/32X EI/ 270 27 3,382,448 5/1968 Oberg et a1. 338/32X [31] 53 and4l 53 1 Continuation-impart of application Ser. No. i p g 1 Barney 661,757, Aug. 4, 1967, now abandoned.

Att0rneyl(urt Kelman ABSTRACT: A solid state element hairing in- [54] gggggg MAGNETORESISTANCE homogeneities in impurity concentration is positioned within a mu 12D Fi magnetic field and experiences changes in resistance when rawmg subjected to energy in the form of a standing sound wave, a [52] U.S.Cl 338/14, travelling sound wave, a change in direction of a ma netic g 338/ 17, 338/32 field, or light in a attern of alternating intensit Patented March 9,1971

4 Sheets-Sheet 1 INVENTOR i-uaov'um UJ|5A A AGENT I Patented I March 9, 1971 3,569,895

4 Shets-Sheet z I NVENTOR mowm :FUJIMDA BY W Patented March 3,569,895

I I 4 Sheets-Sheet s I I mung v w INVENTOR AGENF' Patented March 9,1971 3,569,895

4 Sheets-Sheet 1L INVENTOR INIIOMGGENEOUS MAGNETORESISTANCE DEVICES REFERENCE TO RELATED APPLICATION This is a continuation-in-part of my application Ser. No. 661,757, filed Aug. 4, 1967, now abandoned.

This invention relates to a magnetoresistance device utilizing the sharp angle dependence of the magnetoresistance effeet in a solid state element having layer form inhomogeneities in carrier concentrations. It further relates to a magnetoresistance device utilizing the dependence of the magnetoresistance effect on the degree of inhomogeneities in carrier concentration.

In conventional devices utilizing the magnetoresistance effect, the dependence of electric resistance on the strength of the magnetic field is utilized. However, conventional devices are defective in that sensitivity is low. Furthermore, devices such as transistors, vacuum tubes, and the like are likewise dethe input from the output is impossible and, very often, conventional devices are unusable at high frequencies.

The object of this invention is to provide inhomogeneous magnetoresistance devices for use in amplification, oscillation, waveform conversion, frequency conversion or signal conversion which are of high sensitivity and fully utilizable even in the high frequency region.

The novel features that are considered characteristic of this invention are set forth with particularity in the appended claims.'The invention itself, however, both as to its organization and method of operation, as well as additional objects and advantages thereof, will best be understood from the following description when read in connection with the accompanying drawing wherein:

FIG. I shows an example of a solid state element having layer form inhomogeneities;

FIG. 2 and FIG. 3 each shows a plot of a form in which the impurity concentration changes in the X direction of the structure of FIG. I;

FIG. 4 shows a curve of the angular dependence of the electric resistance of the solid state element illustrated in FIG. 1 for various angles of magnetic field;

FIG. 5 illustrates structure of a device utilizing the sharp angular dependence of the electric resistance of a solid state element having layer form inhomogeneities;

FIGS. 6 to 8 illustrate three kinds of relationships between the input signal and output signal of the device illustrated in FIG. 5;

FIG. 9 shows the change in electric resistance for various degrees of inhomogeneities;

FIGS. 10 and 11 each shows structure in accordance with the principles of this invention for converting a sound wave into an electricsignal; and

FIG. 12 shows structure in accordance with the principles of this invention for converting light into an electric signal.

The term angle" used herein refers to the angle between the direction of the magnetic field and the current direction, i.e. longitudinal direction, of the solid state element. Also, the term "layer form inhomogeneities" refers to the inhomogeneities in structure wherein thin platelike materials which differ in impurity concentration are alternately positioned adjacent to each other (see FIG. 2). When the platelike materials become infinitely thin, the impurity concentration changes continuously in a certain specific direction (see FIG. 3).

As is well known, the magnetoresistance effect (meaning the effect of the change in electric resistance under a magnetic field) of a solid-state element with high electron mobility such small. Accordingly, the cases of utilizing the effect of inhomogeneities are divided into two types, one utilizing the sharp angle dependence under a fixed degree of layer form inhomogeneities in impurity concentration and the other one utilizing the change in resistance caused by changing the degree of inhomogeneities in electron concentration.

FIG. 1 shows an example of the solid state element having layer form inhomogeneities in the longitudinal direction (x direction). The solid and dashed lines in FIG. 1 show the maximum and minimum values of electron concentration, respectively. FIG. 2 and FIG. 3 each shows the form in which the impurity concentration changes in the x direction. The forms shown in FIGS. 2 and 3 are typical examples. However, the impurity concentration need not always change in such forms.

FIG. 4 shows the state of change in electric resistance in the case .where a constant magnetic field is applied to the solid state element illustrated in FIG. 1 while the angle of said magnetic field to the longitudinal direction of said solid state element is changed. In FIG. 4, the solid line curve shows the characteristics in the case where the solid state element has layer form inhomogeneities; and, the dashed line curve shows the characteristics in the case where said element is devoid of said inhomogeneities. FIG. 4 illustrates clearly the effect of layer form inhomogeneities. It is to be noted that in the vicinity of g the angular dependence of electric resistance becomes strikingly great. Accordingly, if a constant magnetic field which is applied at an angle corresponding to the points A, B or C shown in FIG. 4, was changed slightly be some means, a great change in electric resistance would be obtained.

FIG. 5 shows an embodiment changing the angle of a magnetic field electrically. Solid state element 1 having layer form inhomogeneities is in a constant bias magnetic field applied by a permanent magnet or electromagnet 2. Coil 4 is adapted to excite a magnetic field in the longitudinal direction of the solid state element 1. Now, if an input signal voltage Vin" is applied to the coil 4, the direction of resultant magnetic field slightly changes because the magnetic field generated by the coil 4 differs in direction from the constant bias magnetic field. As already stated, the electric resistance between the electrodes 3, 3' of solid state element 1 tends to change easily by the change in the direction of a magnetic field. Therefore, this electric resistance changes greatly according to the input signal. When a voltage source 5 is connected through a load resistance 6 between the electrodes 3, 3', an output signal voltage Vout is produced across said load resistance.

The above embodiment can be applied to various uses by selecting an appropriate angle go of the bias magnetic field relative to the longitudinal direction of the solid state element 1.

FIGS. 6 to 8 each shows the relationship between the input signal and the output signal in the case where the angle L0 is set to correspond to the respective points A, B and C in FIG. 4. In FIG. 6 a bias magnetic field is applied in the direction in which the angular dependence is greatto produce a great change in resistance with a small amount of input signal voltage Vin". This embodiment finds application in an amplifier.

In FIG. 7 a bias magnetic field is applied in the direction in which the resistance is greatest. This embodiment finds application in a frequency multiplier. In FIG. 8, by applying a bias magnetic field to the point C where the angular dependence is small it is possible to convert the input voltage of rectangular wave form into an output voltage of sharp pulse form. In addition to the embodiments shown, it is also possible, by utilizing the angle dependence of the layer form inhomogeneous magnetoresistance effect, to effect conversion of various other waveforms and frequencies. Further, the embodiments illustrated can be utilized as highly sensitive variable resistance elements in various electric circuits.

The structure of FIG. 5, when positioned to utilize the sharp angle dependence exhibits high amplification characteristic. Because of this high sensitivity, there are many advantages. The gains of amplifiers and the conversion efficiencies of waveform converters or frequency converters can be made very high. Also, when an input signal is fed to the invention as illustrated in FIG. 5, complete isolation is obtained between the input signal and the output signal.

FIG. 9 illustrates the change in electric resistance in the case where the degree of inhomogeneities is changed under constant magnetic field B In this instance, the inhomogeneities need not always be in layer form. In the plot of FIG. 9, n, represents the mean value of the carrier concentrations: An, represents the deviation from said means value,

represent the means value of (An)? Accordingly, the abscissa is a standard deviation of the carrier concentration. B B and 13, each represents a certain specific value of bias magnetic field 3,. Since B,,, B,, B,, the stronger the bias magnetic field, the greater the effect of inhomogeneities. If inhomogeneities are formed in the carrier concentration by an input signal, a change in resistance of the solid state element will result and the output can be obtained as an electric signal.

FIGS. 10 and 11 each illustrates an embodiment where the degree of layer form inhomogeneities is changed by a sound wave to convert a sound wave into an electric signal. Referring specifically to FIG. 10. A sound wave is introduced through a sound wave conducting medium 9 into an end of a homogeneous solid state element 7 having an electron of high mobility such as lnSb, the other end of said solid state element being connected to a mismatching load 8. The sound wave then propagates in standing wave form in the solid state element, and, due to the interaction between the sound wave and the electron, the electron concentration changes not only as time elapses but even spacially with the same periodicity as the sound wave. In this case, because the sound wave is in standing wave form, the electron concentration is also in standing wave form. The degree of inhomogeneities changes at a frequency that is double (2 times) that of the sound wave, where An is a deviation from the mean value n, of electron concentration. Accordingly, if a constant bias magnetic field is applied to the solid state element 7 by a permanent magnet or electromagnet 2, the electric resistance between the

electrodes

3, 3 changes at a frequency double (2 times) that of the sound wave. If an electric current is constantly applied from a voltage source 5 through a load resistance 6 to the electrodes 3, 3', the voltage at both ends of said load resistance changes at a frequency that is double (2 times) that of the sound wave, and this change in voltage can be detected by a detector means 10.

FIG. 11 illustrates an embodiment using a matching load 8 in place of the mismatching load 8 in FIG. 10. In this case, the sound wave is in travelling wave form in the solid state element, and, accordingly, the electron concentration is also in travelling wave form. The degree of inhomogeneities in electron concentration does not change as time elapses, but the electric resistance alone between the electrodes 3, 3' changes according to the input sound wave. The change in resistance between the

electrodes

3, 3 can be detected by a detector means 14 through the bridge network in which the solid state element 7 is set as one of the arms thereof.

The solid and dashed lines on the respective solid state elements 7 in FIGS. 10 and 11 show the maximum and minimum values of space distribution of electron concentration at a specific instant of time.

FIG. 12 illustrates an embodiment changing the degree of inhomogeneities in electron concentration by light to convert light into an electric signal. Solid state element 18 is disposed in inclined form so that both a magnetic field excited by a permanent magnet or electromagnet 2 and light may be applied simultaneouslyto said solid state element. A light shield plate 19 with interstices is mounted onthe solid state element 18 so that light may be applied only to a portion of said solid state element. When light is applied through said shield plate to the solid state element 18, the electron concentration increase only in those portions of said element that are exposed to the light. Accordingly, the degree of inhomogeneities in electron concentration and consequently the resistance between the

electrodes

3, 3 located at both ends of the solid state element 18 disposed in the magnetic field increases. This increase in resistance due to the application of light can be detected by a detector means 14 of the bridge network in which the solid state element 18 is set as an arm thereof.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is, therefore, to be understood that the invention may be practiced otherwise than as specifically described herein.

I claim:

1. A magnetoresistance device comprising a solid state element having layer form inhomogeneities in impurity concentration, means to apply a constant bias magnetic field to said solid state element, a coil to generate a second magnetic field which differs in direction from said constant bias magnetic field to change the direction of resultant magnetic field, the resistance of said solid state element being determined by the direction of said resultant magnetic field.

2. The structure of claim 1 wherein said means to apply a constant bias magnetic field to said solid state element comprises a magnet.

3. The structure of claim 1 wherein said solid state element is oriented to said constant bias magnetic field to exhibit a maximum angular dependence of resistance.

4. The structure of claim 3 including means sensitive to changes in the resistance of said solid state element.

5. The structure of claim 4 wherein said means sensitive to changes in the resistance of said solid state element comprises a source of potential coupled to said solid state element, and a load impedance coupled to exhibit changes of potential across said solid state element.

6. The structure of claim 1 wherein said solid state element is disposed within and oriented to said constant bias magnetic field to exhibit a maximum resistance.

7. A magnetoresistance device for converting a sound wave into an electric signal comprising a magnet for supplying a constant magnetic field, a solid state element having layer form inhomogeneities in impurity concentration and positioned within said magnetic field, means for introducing a sound wave to one of said opposing ends of said solid state element, load means for said sound wave coupled to the other of said opposing ends of said solid state element wherein the resistance of said solid state element is changed by the introduction of a sound wave to the opposing end, and means coupled to detect changes in the resistance of said solid state element.

8. The structure of claim 7 wherein said load means comprises a mismatching load for said sound wave to generate the standing sound wave in said solid state element whereby the resistance of said solid state element changes at a frequency double that of the sound wave and said means coupled to detect changes in the resistance of said solid state element generates a signal having a frequency double that of the sound wave.

9. The structure of claim 7 wherein said load means comprises a matching load for said sound wave to generate the travelling sound wave in said solid state element.

10. A magnetoresistance device for converting light into an electric signal comprising a magnet for supplying a constant magnetic field, a solid state element having layer form inhomogeneities in impurity concentration and positioned within said magnetic field, element, a light shield plate interposed between said solid state element and said means and having interstices adapted to pass light only to a portion of said solid state element, and means for detecting changes in resistance of said solid state element due to the inhomogeneities in electron concentration of said solid state element caused by the partial application of light to said solid state element.