Abstract:
A micro magnetic core memory having a magnetic core, which serves as a storage medium, a coil, which is located in close vicinity to the magnetic core and magnetizes the magnetic core, and a sensor, which is located in close vicinity to the magnetic core and detects polarity of magnetization of the magnetic core. The micro magnetic core memory has the effects in that the inputting and the outputting of information can be carried out quickly, in that a high degree of integration can be achieved easily and a storage device having a large capacity can be produced at a low cost, and in that the stored information is not lost when the supply of electric power is turned off.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a memory cell, which is formed on a semiconductor substrate constituted of silicon, or the like. This invention also relates to a method of inputting and outputting information. 
     2. Description of the Prior Art 
     With the increased use of the Internet in recent years, there has arisen a strong demand for computers, particularly personal computers (hereinbelow referred to as the “PC”), and rapid advances have been made in the related techniques. Also, the market requires products, which have as high a performance as possible and are as cheap as possible, and research has continuously been carried out in order to satisfy the requirements of the market. 
     One of important factors for determining the performance of computers is a storage device. Currently popular storage devices are semiconductor storage devices, which comprise a semiconductor substrate constituted of silicon, or the like, and memory cells formed on the semiconductor substrate. In order for a storage device to have a high performance, the storage device should primarily satisfy the requirements in that the inputting and the outputting of information can be carried out quickly, in that the memory should have a large capacity, and in that the stored information can be retained with a high stability. It will be possible for computers to take constitutions in accordance with various requirements of the market. However, if both of the requirements for the quick operation and the large capacity are to be satisfied, the cost cannot be kept low. The cost can be kept low by compromising on either one of the two requirements. 
     In the currently most popular main body memories of PC&#39;s, cache memories and main memories are constituted of random access memories (RAM&#39;s). As the RAM&#39;s, dynamic random access memories (DRAM&#39;s) and static random access memories (SRAM&#39;s) are used. 
     The DRAM&#39;s have a larger capacity per unit area than SRAM&#39;s and can be produced at a low cost. However, the DRAM&#39;s have the drawbacks in that, since the takeout of stored information is carried out by the discharging of electric charges, a long time is required to output the stored information, and electric charges must always be supplied (refreshed). With the SRAM&#39;s, the takeout of stored information is carried out by the discrimination of the state of a multivibrator. Therefore, with the SRAM&#39;s, refreshing operations need not be carried out, and the stored information can be read quickly. However, the SRAM&#39;s have the drawbacks in that, due to their complicated structures, the capacity per unit area is smaller than in the DRAM&#39;s, and the cost cannot be kept low. 
     Accordingly, in an ordinary constitution of PC memories, the SRAM&#39;s are employed as the cache memories, the DRAM&#39;s are employed as the main memories, and the cost is thereby restricted. 
     Also, with the DRAM&#39;s and the SRAM&#39;s, the stored information is lost when the electric power source is turned off, and therefore necessary information must be stored on other storage devices, such as disks. Memories, which have the characteristics such that the stored information may not be lost when the electric power source is turned off, include flash memories. However, due to the necessity of a high voltage for the information inputting operation, a limitation on the capacity, and the cost, the flash memories cannot sufficiently satisfy the aforesaid requirements of the current market. 
     SUMMARY OF THE INVENTION 
     The primary object of the present invention is to provide a micro magnetic core memory, which serves as a memory cell constituting a storage device capable of satisfying requirements for a main body RAM of a computer in that the inputting and the outputting of information can be carried out quickly, in that a high degree of integration can be achieved easily and a storage device having a large capacity can be produced at a low cost, and in that the stored information can be retained with a high stability without being lost when the supply of electric power is turned off. 
     Another object of the present invention is to provide a method of inputting and outputting information, in which the micro magnetic core memory is utilized. 
     The present invention provides a micro magnetic core memory, comprising: 
     i) a magnetic core, which serves as a storage medium, 
     ii) a coil, which is located in close vicinity to the magnetic core and magnetizes the magnetic core, and 
     iii) a sensor, which is located in close vicinity to the magnetic core and detects polarity of magnetization of the magnetic core. 
     The present invention also provides a method of inputting and outputting information, comprising the steps of: 
     i) employing a magnetic core, which is a magnetic material, as a storage medium, 
     ii) locating at least one coil with respect to one magnetic core, the coil serving to magnetize the magnetic core, 
     iii) magnetizing the magnetic core by the coil, information being thereby written into the magnetic core, 
     iv) locating at least one sensor with respect to one magnetic core, the sensor serving to detect polarity of magnetization of the magnetic core, and 
     v) detecting the polarity of magnetization of the magnetic core by the sensor, the stored information being thereby read from the magnetic core. 
     The micro magnetic core memory in accordance with the present invention serves as a memory cell for constituting a storage device, which takes on the form of an RAM primarily like a DRAM and a SRAM. The micro magnetic core memory in accordance with the present invention has the same advantages as those of the DRAM and the SRAM. Also, with the micro magnetic core memory in accordance with the present invention, as in a flash memory, the stored information is not lost when the electric power source is turned off. 
     Therefore, in the method of inputting and outputting information, the magnetic core is employed as a storage medium, at least one coil is located with respect to one magnetic core, the magnetic core is magnetized by the coil, and information is thereby written into the magnetic core. Further, at least one sensor is located with respect to one magnetic core, the polarity of magnetization of the magnetic core is detected by the sensor, and the stored information is thereby read from the magnetic core. 
     In a fundamental constitution of the memory cell, the coil may be wound around the magnetic core, and the sensor may be located in close vicinity to the magnetic core. As the sensor, a thin-film sensor, such as a giant magnetic resistor (GMR) or a magnetic resistor (MR), which is easy to process and has a high resolution, may be employed. 
     Accordingly, the micro magnetic core memory in accordance with the present invention has the simple structure and does not require complicated structures, such as trenches and stacks. Thus the micro magnetic core memory in accordance with the present invention can be easily integrated to a high degree and can constitute a large-capacity RAM device at a low cost. 
     In cases where a storage device is produced by integrating the micro magnetic core memory in accordance with the present invention, for example, the magnetic material of a silicon crystal, such as garnet, is appropriate as the material of the magnetic core. Also, as the thin-film sensor for reading the stored information, the GMR or the MR is appropriate. Therefore, mass production of the storage device can be carried out with approximately the same processes as those for the conventional LSI&#39;s, and the like. 
     The micro magnetic core memory in accordance with the present invention has good effects in that it can constitute the storage device having the performance described below. 
     (1) The inputting and the outputting of information can be carried out quickly. 
     (2) A high degree of integration can be achieved easily, and a storage device having a large capacity can be produced at a low cost. 
     (3) The stored information is not lost when the supply of electric power is turned off. 
     The storage device utilizing the micro magnetic core memory in accordance with the present invention can be used for the same purposes as those of the conventional DRAM&#39;s and SRAM&#39;s and can also be applied as various kinds of micro chips by the utilization of the characteristics of the storage device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an enlarged perspective view showing an embodiment of the micro magnetic core memory in accordance with the present invention, 
     FIG. 2 is an explanatory view showing a constitution of a storage device utilizing the micro magnetic core memory in accordance with the present invention, 
     FIG. 3 is a plan view showing a different embodiment of the micro magnetic core memory in accordance with the present invention, 
     FIG. 4 is a sectional view showing the embodiment of FIG. 3, 
     FIG. 5 is a plan view showing a further different embodiment of the micro magnetic core memory in accordance with the present invention, and 
     FIG. 6 is a sectional view showing the embodiment of FIG.  5 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The present invention will hereinbelow be described in further detail with reference to the accompanying drawings. 
     FIG. 1 is an enlarged perspective view showing an embodiment of the micro magnetic core memory in accordance with the present invention. FIG. 2 is an explanatory view showing a constitution of a storage device utilizing the micro magnetic core memory in accordance with the present invention. 
     As illustrated in FIG. 1, an embodiment of the micro magnetic core memory in accordance with the present invention comprises a magnetic core  1  having an approximately cylindrical shape, and a coil  3 , which is wound around the outer periphery of the magnetic core  1  and magnetizes the magnetic core  1 . The micro magnetic core memory also comprises a writing row line  31  and a writing column line  32 , which are connected to the coil  3 . The micro magnetic core memory further comprises a sensor  2 , which is located in close vicinity to the side of the magnetic core  1  and detects the polarity of magnetization of the magnetic core  1 . The micro magnetic core memory still further comprises a reading row line  21  and a reading column line  22 , which are connected to the sensor  2 . In FIG. 1, reference numerals  25  and  35  represent via-holes for connection. 
     As illustrated in FIG. 2, the sensor  2  is connected to a reading driver  23  via the reading row line  21  and is connected to a reading sense amplifier  24  via the reading column line  22 . In accordance with instructions given from the reading driver  23  and the reading sense amplifier  24 , the sensor  2  detects the polarity of magnetization of the magnetic core  1 . In cases where a thin-film sensor, which is constituted of a magnetic resistance element, is employed as the sensor  2 , it becomes easy to form an integrated circuit. Therefore, a GMR or an MR should preferably be employed as the material for the sensor  2 . 
     As illustrated in FIG. 2, the coil  3  is connected to a writing driver  33  via the writing row line  31  and is connected to a writing control amplifier  34  via the writing column line  32 . In accordance with instructions given from the writing driver  33  and the writing control amplifier  34 , the coil  3  magnetizes the magnetic core  1 . As a result, the polarity of magnetization of the magnetic core  1  is changed. 
     With the technique for detecting the polarity of magnetization by the magnetic resistance element, which serves as the sensor, and thereby reading the stored information, instead of the reading of the stored information being carried out by the receiving of electric charges as in the DRAM&#39;s, the reading of the stored information can be carried out by merely detecting the polarity of magnetization. Therefore, with the storage device utilizing the micro magnetic core memory in accordance with the present invention as the memory cell, the outputting of the stored information can be carried out very quickly, for example, within approximately 10 nanoseconds. 
     As illustrated in FIG. 2, in the storage device utilizing the micro magnetic core memory in accordance with the present invention, a plurality of magnetic cores  1   a ˜ 1   n  are located on a semiconductor substrate  4 . Also, sensors  2   a ˜ 2   n  and coils  3   a ˜ 3   n  are located respectively in close vicinity to the corresponding magnetic cores  1   a ˜ 1   n . Specifically, for example, the sensor  2   a  and the coil  3   a  are located in close vicinity to the corresponding magnetic core  1   a.    
     The sensors  2   a ˜ 2   n  are connected to the reading driver  23  via the corresponding reading row lines  21   a ˜ 21   n . Also, the sensors  2   a ˜ 2   n  are connected to the reading sense amplifier  24  via the corresponding reading column lines  22   a ˜ 22   n . The coils  3   a ˜ 3   n  are connected to the writing driver  33  via the corresponding writing row lines  31   a ˜ 31   n . Also, the coils  3   a ˜ 3   n  are connected to the writing control amplifier  34  via the corresponding writing column lines  32   a ˜ 32   n.    
     When the information is to be written into one of the magnetic cores  1   a ˜ 1   n , one of the writing row lines  31   a ˜ 31   n  is selected by the writing driver  33 , and one of the writing column lines  32   a ˜ 32   n  is selected by the writing control amplifier  34 . In this manner, one of the magnetic cores  1   a ˜ 1   n  is selected, and the information is written into the selected magnetic core. When the stored information is to be read from one of the magnetic cores  1   a ˜ 1   n , one of the reading row lines  21   a ˜ 21   n  is selected by the reading driver  23 , and one of the reading column lines  22   a ˜ 22   n  is selected by the reading sense amplifier  24 . In this manner, one of the magnetic cores  1   a ˜ 1   n . In is selected, and the stored information is read from the selected magnetic core. 
     By way of example, in the writing operation, the writing row line  31   e  is selected by the writing driver  33 , and the writing column line  32   e  is selected by the writing control amplifier  34 . In this manner, the polarity of magnetization of the magnetic core  1   a  is changed by the coil  3   e , and the information is thereby written into the magnetic core  1   e.    
     Also, by way of example, in the reading operation, the reading row line  21   a  is selected by the reading driver  23 , and the reading column line  22   a  is selected by the reading sense amplifier  24 . In this manner, the polarity of magnetization of the magnetic core la can be read by the sensor  2   a.    
     FIG. 3 is a plan view showing a different embodiment of the micro magnetic core memory in accordance with the present invention. FIG. 4 is a sectional view showing the embodiment of FIG.  3 . In FIG.  3  and FIG. 4 (and those that follow), similar elements are numbered with the same reference numerals with respect to FIG.  1 . 
     Ordinarily, problems are of ten encountered in that several types of sensors cannot accurately detect the polarity of magnetization. In order for such problems to be eliminated, in the embodiment of FIG. 3, a magnetic bias coil  3 ′, which can apply a magnetic bias, is employed as the coil for magnetizing the magnetic core  1 . When information is to be written into the magnetic core  1 , the magnetic bias coil  3 ′ magnetizes the magnetic core  1  by applying a bias in a certain direction. As a result, the total amount of magnetization of the magnetic core  1  changes, depending upon the polarity, while the polarity itself, with which the magnetic core  1  is to be magnetized, is not being changed. Specifically, in cases where the direction of the bias coincides with the polarity, with which the magnetic core  1  is to be magnetized, the total amount of magnetization of the magnetic core  1  becomes large. In cases where the direction of the bias is reverse to the polarity, with which the magnetic core  1  is to be magnetized, the total amount of magnetization of the magnetic core  1  becomes small. Therefore, the polarity of magnetization of the magnetic core  1  can be detected accurately. In FIG. 3, reference numeral  2 ′ represents a sensor, such as a GMR. 
     FIG.  5  and FIG. 6 show a further different embodiment of the micro magnetic core memory in accordance with the present invention. In this embodiment, a magnetic bias coil  3 ″, which is of the same type as the magnetic bias coil  3 ′ shown in FIG. 3, is employed. Also, asensor  2 ″ constituted of a semiconductor device is employed as the sensor. As illustrated in FIG. 6, the sensor  2 ″ may be located at the lower part of the micro magnetic core memory. The application of the magnetic bias is effective not only when the sensors cannot accurately detect the polarity of magnetization, but also when sensors of low sensitivity are used.