Abstract:
A magnetically sensitive semiconductor includes an emitter electrode, at least three collector electrodes arranged substantially equidistantly from the emitter electrode and spaced apart substantially equidistantly in order to extract carriers outputted by the emitter electrode and migrating through a semiconductor, and first base electrodes for accelerating the carriers in the direction of the collector electrodes from the emitter electrode, the collector electrodes at both ends of the at least three collector electrodes serving as collector output electrodes. By virtue of such an arrangement, carriers unnecessary for field detection are eliminated to provide a magnetically sensitive semiconductor having excellent sensitivity.

Description:
This application is a continuation of application Ser. No. 07533,491, filed June 5, 1990, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a lateral-type magnetically sensitive semiconductor device. 
     2, Description of the Prior Art 
     A magnetically sensitive semiconductor which detects the strength of a magnetic field by a difference current between two collector electrodes is known in the art. FIGS. 3A through 3C are diagrams illustrating the operating principle of an ordinary magnetically sensitive semiconductor. In the case illustrated, the carriers of the semiconductor are electrons (i.e., the semiconductor is an npn transistor), the equivalent circuit of which is shown in FIG. 3C. In general, a magnetically sensitive semiconductor has a specific sensitivity S expressed by ΔI C  /I CO  ·ΔB, where ΔI C  represents the difference current between two collectors, I CO  the collector current when a magnetic field B=0, and ΔB an amount of change in the magnetic field. 
     FIG. 3A illustrates a state in which the magnetic field B is not being applied. At such time the amounts of electrons which reach collectors C1, C2 from an emitter E are substantially equal, and therefore the collector currents are equal (IC 1  =IC 2 ). Accordingly, the difference current ΔI C  between the two collectors is zero. By contrast, FIG. 3B illustrates a state in which the magnetic field B is applied perpendicularly to the transistor. Here the direction of electron migration is curved as shown in the diagram owing to a Lorentz force produced by the magnetic field B, as a result of which the amount of electrons reaching the collector C1 is greater than that reaching the collector C2. In other words, the collector current IC 1  becomes greater than the collector current IC 2 . Thus, the strength of the magnetic field B is obtained in accordance with B ∝ΔI C  (difference current)=IC 1  -IC 2  &gt; 0. By changing the potentials of the bases B, the field detection characteristic can be made linear and the collector current can be amplified. 
     In a magnetically sensitive semiconductor device having such a construction, it is desired that only carriers affected by the magnetic field be injected into the collectors. However, the magnetically sensitive semiconductor device having the conventional construction is such that carriers unnecessary for field detection also are injected into the two collectors Cl, C2, as a result of which accurate field detection cannot be carried out. In actuality, moreover, all of the carriers influenced by the magnetic field are not injected into the collectors Cl, C2; some flow out from both sides of the emitter. For this reason, the magnetic field cannot be measured accurately. Furthermore, it is required that the lengths of carrier migration (the distances from the emitter to the collectors) are made sufficiently large in order to detect the influence of the magnetic field. However, when these distances are lengthened, the number of carriers reaching the collectors diminishes and sensitivity declines. 
     SUMMARY OF THE INVENTION 
     The present invention has been devised in view of the foregoing problems of the prior art, and its object is to provide a magnetically sensitive semiconductor device so adapted that carriers unrelated to field detection will not flow into collector output electrodes, thereby raising field detection accuracy. 
     Another object of the present invention is to provide a magnetically sensitive semiconductor device in which carriers affected by a magnetic field are prevented from flowing out. 
     According to the present invention, the foregoing objects are attained by providing a magnetically sensitive semiconductor device for outputting a difference current between two collector electrodes in conformity with the strength of an applied magnetic field, comprising an emitter electrode, at least three collector electrodes arranged substantially equidistantly from the emitter electrode and spaced apart substantially equidistantly in order to extract carriers outputted by the emitter electrode and migrating through a semiconductor, and a first base electrode for accelerating the carriers in the direction of the collector electrodes from the emitter electrode. 
     In a preferred embodiment of the present invention, the magnetically sensitive semiconductor device further comprises a second base electrode provided on both sides of a path of migration of the carriers from the emitter electrode to the collector electrodes. 
     Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1A is a diagram illustrating the construction of a pnp-type magnetically sensitive semiconductor device according to an embodiment of the present invention; 
     FIG. 1B is an equivalent circuit diagram of the transistor of FIG. 1A; 
     FIG. 2A is a diagram illustrating the construction of an npn-type magnetically sensitive semiconductor device according to an embodiment of the present invention; 
     FIG. 2B is an equivalent circuit diagram of the transistor of FIG. 2A; and 
     FIGS. 3A through 3C are diagrams illustrating the operating principle of a magnetically sensitive semiconductor device according to the prior art, in which: 
     FIG. 3A is a diagram showing the flow of carriers in the absence of an applied magnetic field; 
     FIG. 3B is a diagram showing the flow of carriers in the presence of a magnetic field B; and 
     FIG. 3C is an equivalent circuit diagram of the prior-art magnetically sensitive semiconductor device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     A preferred embodiment of the present invention will now be described in detail with reference to the accompanying drawings. 
     Description of the Magnetically Sensitive Semiconductor Device 
     (FIGS. 1 and 2) 
     FIGS. 1A, 1B, 2A and 2B are diagrams showing the construction of lateral-type magnetically sensitive semiconductors of the embodiment, as well as the equivalent circuits thereof. Specifically, FIGS. 1A and 1B illustrate a lateral-type pnp magnetically sensitive semiconductor for measuring the strength of a magnetic field acting in a direction perpendicular to the plane of the drawing, and FIGS. 2A and 2B similarly illustrate a lateral-type npn magnetically sensitive semiconductor for measuring the strength of a magnetic field acting in a direction perpendicular to the plane of the drawing. 
     In Fig. 1A, numeral 11 denotes a cross section taken along line A--A&#39; of a magnetically sensitive semiconductor 10. The magnetically sensitive semiconductor 10 has an emitter E, collectors C1, C2 and bases B1, B4 which correspond to the emitter E, collectors C1, C2 and bases B of the prior-art magnetically sensitive semiconductor shown in FIG. 3. 
     To fabricate the magnetically sensitive semiconductor 10, an n-type epitaxial layer 13 is grown on a p-type substrate 12, and an n +  layer is diffused to form bases B1 through B4 (14 through 17). Further, a p-type emitter E (18) and collectors C1 through C3 (19 through 21) are formed as illustrated by base boron diffusion or the like. Numerals 22, 23 denote insulative isolating walls formed by boron diffusion. 
     By virtue of the foregoing construction, carriers (holes) from the emitter 18 are accelerated toward the collectors 19 through 21 by the bases B1 and B4. Since the bases B2, B3 (16, 17) provided on both ends of the emitter 18 are of n +  conductivity type, the carriers (holes) recombine at the base portions 16, 17. This occurs even in a case where the bases 16, 17 do not possess a potential with respect to the emitter 18. As a result, it is possible to suppress the flow of carriers, which are unnecessary for field detection, on the outer sides of the bases 16, 17. 
     Conversely, if a voltage is applied to the bases 16, 17 that is the reverse of the voltage at the emitter 18, a depletion layer can be formed between the emitter 18 and the bases 16, 17. Consequently, the flow of carriers (holes) from the emitter 18 toward the bases 16, 17 can be blocked completely. As a result, sufficient carriers necessary for field detection can be delivered from the emitter 18 to the collectors 19 through 21. 
     On the collector side, the collector C3 (20) is provided between the collectors C1, C2 (19, 21). Carriers necessary for field detection reach the collectors 19, 21 to be detected thereof and are sufficient in number. Carriers which head straight for the collector 20 from the emitter 18 are unnecessary for field detection. Accordingly, these superfluous carriers are extracted by the collector C3 (20) and have no effect upon the detection of the magnetic field by the collectors C1, C2. 
     FIG. 1B illustrates the equivalent circuit of the npn-type magnetically sensitive semiconductor 10. The transistor 10 can be comprised by two pnp transistors whose emitters E, bases B1, B4 and collectors C3 are commonly connected. The bases B2, B3 can be short-circuited to form a single base. 
     FIGS. 2A, 2B are diagrams showing the construction of a pnp-type magnetically sensitive semiconductor, which is obtained by reversing the polarity of each of the portions of the pnp-type magnetically sensitive semiconductor of FIG. 1, as well as the equivalent circuit thereof. 
     In FIG. 2A, numeral 41 denotes a cross section taken along line C--C&#39; of a magnetically sensitive semiconductor 41. 
     To fabricate the magnetically sensitive semiconductor 40, an n-type epitaxial layer 43 is grown on a p-type substrate 42, and a p-type layer 55 is formed thereon by base boron diffusion. An n+layer is diffused on the p-type layer portion 55 to form an emitter E48 and collectors C1 through C3 (49 through 51). Further, the p-type layer portion 55 is provided with bases B1 through B4 (44 through 47), as shown. Numerals 52, 53 denote insulative isolating walls formed by boron diffusion. 
     Whereas the carriers in the case of FIG. 1 are holes, the carriers in FIG. 2A are electrons. This is the only difference between the two. Since the basic operating principle is the same, this will be described in simple terms. 
     The base B1 (44) and base B4 (45) are provided in order to accelerate the carriers (electrons) migrating from the emitter 48 to the collectors 49 through 51, and the bases B2, B3 (46, 47) are provided in order to prevent carriers unrelated to field detection from flowing in. The collector C3 (50) is for extracting carriers which are not influenced by a magnetic field. This prevents a decline in field detection accuracy caused by these carriers flowing into the collector C1 or C2. 
     FIG. 2B is a diagram showing the equivalent circuit of this pnp-type magnetically sensitive semiconductor. This can be constructed by joining two npn transistors whose emitters E, bases B1, B4 and collectors C3 are commonly connected. 
     The present embodiment has the following advantages: 
     (1) An additional collector is provided between two other collectors, and carriers unnecessary for field detection are eliminated by this collector, thereby making it possible to raise field detection sensitivity. 
     (2) A reduction in the number of carriers influenced by the magnetic field can be prevented by suppressing the migration of carriers from the emitter toward the periphery of the transistor element. As a result, sensitivity is improved. 
     (3) Bases are provided on both sides of the path along which carriers migrate from the emitter to the collector side, and a voltage opposite that of the emitter is applied to these bases. As a result, the path of carrier migration is narrowed to make possible an improvement in sensitivity. 
     Thus, in accordance with the present embodiment, a minute magnetic field can be detected in conjunction with high stability. Accordingly, the magnetically sensitive semiconductor of the invention is applicable also to an acceleration sensor capable of sensing acceleration from a DC component to an AC component. 
     Further, since the magnetically sensitive semiconductor of the present embodiment is a lateral-type magnetic sensitive semiconductor formed in silicon by a bipolar process, it can be fabricated on a single chip as a signal processing circuit. The magnetically sensitive semiconductor lends itself also to the development of intelligent sensors which include other control circuits. 
     Though three collectors are arrayed in a straight line in the foregoing embodiment, this is not a limitation upon the present invention, for the collectors can be arrayed equidistantly along the circumference of a circle whose center is the emitter. The number of collectors and the number of bases are not limited to those in the above-described embodiment. 
     As many apparently widely different embodiments of the present invention can be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited to the specific embodiments thereof except as defined in the appended claims.