Patent GB-1389472-A (GB)
Title: Magneto-sensitive device having pn junction
IPC: H01L29/82
Filed: 1972-05-26
Abstract: 1389472 Magnetosensitive devices MATSUSHITA ELECTRIC INDUSTRIAL CO Ltd 26 May 1972 [26 May 1971] 24953/72 Heading H1K A magnetosensitive PN junction device comprises an e.g. silicon monocrystal having an N-type region into which a P-type region is inset, whose top surface is covered with an insulant e.g. silicon dioxide layer having four apertures positioned at the respective ends of the P and N regions. Two pairs of electrodes are formed on the insulant to ohmically contact the ends of the PN regions through the apertures, and the PN junction between the regions defines a depletion layer (Figs. 1A, 1B, not shown). A current I flows through the N region between the electrodes thereof and a magnetic field H is applied normal to the current flow and parallel to the PN junction and it is shown (Fig. 2, not shown) that the depletion layer is moved towards the PN junction so as to decrease the conductance of the P region in accordance with H or I, which is detectable by application of D.C. voltage to the electrodes of that region. In a modification (Figs. 3A, 3B) a monocrystalline e.g. Si body 20 has an electrode 21 on one surface and includes a P+ region 22 adjacent thereto, a P region 23, and a U-shaped N region therein surrounding a P-type channel portion 25. A P+ region 26 lies adjacent the channel portion and to the remaining surface 20, which is covered by an insulant layer 27 with apertures 28, 29, 30. Electrode 31 ohmically contacts P + region 26 and one end of N region 24 through apertures 28, 29 and electrode 30 contacts the other end of the N region through aperture 30. A depletion layer forms adjacent the PN boundary and direct current I flows between electrodes 21, 32 through 24, 26, 25 and 22. A magnetic field H deflects the current carrying electrons from the PN junction to widen and increase conductance of channel 25 to further increase current I, which itself increases the deflected electrons to further increase the channel conductance; whereby variations of the field H are converted into amplified variations of I with positive feedback. In further modifications (Figs. 4, 5, not shown) pluralities of the devices of Figs. 3A, 3B are formed in single semiconductor wafer and connected in parallel to electrodes. The impurity concentrations of the several regions and the voltage and current characteristics in terms of applied field are illustrated (Figs. 6, 7, 8, not shown). In a further modification (Figs. 9A, 9B) a P layer 60 is formed on a P substrate 61 to surround an epitaxial N region 62 into which a P region 63 is diffusedly inset having a further N+ region 64; the surface being covered with an insulant layer 65 of silicon oxide or nitride apertured at 66, 67, 68. Vacuum deposited or sputtered aluminium electrode 69 is ohmically connected through aperture 66 to region 62 and through aperture 67 to region 63, while electrode 70 is ohmically connected through aperture 68 to N+ region 64. N+ regions 71 are formed between regions 61, 62 to reduce the resistivity of 62 through which an operative current flows, and a PN junction is formed between 62, 63 so that regions 62, 63, 64 correspond to collector, base, and emitter of a planar transistor. Direct voltage produces current flow in sense 72 through electrodes 69, 70 so that electrons flow in region 62 in sense 73. Magnetic field in direction H causes the electron flow to approach the PN junction and increase the conductance of region 63 according to field intensity, whereby current across the PN junction increases, and the current in region 62<1> increases to an amplified extent. The impurity concentrations are illustrated (Fig. 10, not shown). In a further modification (Figs. 11A, 11B, 12) a magnetsensitive device as shown in Figs. 9A, 9B is formed as an integrated circuit in a P substrate with a PNP and a NPN transistor connected in cascade with integral conductive and resistive regions and overlying aluminium conductors formed by evaporation and photo-etching. A brushless D.C. motor employing the invention (Fig. 13) comprises a tubular cylindrical stationary core 120 internally carrying quadrature spaced coils 121, 122, 123, 124 and quadrature spaced magnetosensitive devices 125, 126, 127, 128. Cylindrical motors 129, 130 with magnetic polarities indicated by arrow 131 are axially rotatable within the core. Each device 125, 126, 127, 128 is D.C. energized and connected in series with an associated coil 121, 122, 123, 124, and responds sequentially in response to the successive magnetic fields to rotate the rotors by successive angles of #/2 so as to produce continuous rotation in the direction 132 without commutation.