Experimental evidence of a novel magneto-sensitive effect in conducting materials
The principle of operation of all semiconductor magneto-sensitive sensors and microsensors is based mainly on the well-known Hall Effect discovered in 1879.
The Hall effect is the generation of an electrical transverse voltage VH across a parallelepiped conductor sample carrying an electric current Is and exposed to an external perpendicular magnetic field ?. The magnitude of the voltage VH, known also as Hall voltage, is given by: VH = (1/qn)(IS.B)(1/d), where q is the charge of the electrons or halls (depend on the type of conductivity of the material – n or p), n is the concentration of the charge carriers in material (mainly semiconductor), d is the thickness of the sample towards the external perpendicutablishedlar magnetic field ?. Change in the polarity of the current IS or of the magnetic field ? causes change of the sign of the signal VH. In 1983, in BAS, Ch.
Roumenin generalized the Hall phenomenon for structures with arbitrary shape and arbitrary orientations of current and magnetic field, and experimentally confirmed presence of Hall voltage in such structures. The so-called parallel magnetic-field Hall effect appears to be very promising for the purposes of microelectronics, in cases when all contacts are planar and the field ? is parallel to the silicone chip plane. The invention of the distinguished American scientist Edwin Hall in 1879 was intended to prove experimentally that magnetic field interacted with moving charge carriers, i.e. when electrical current flowed through the sample, but not with the conductor material itself, as the famous James Maxwell considered. Regardless of the kind of the experimental setup intended for Hall effect investigations, two opposite or planar contacts are always formed, where the voltage VH was generated.
Namely the Hall effect is the fundamental physical phenomenon which, due to its clear linear dependence of the output VH on the current IS and field B, produced simultaneously exact responses about the sign of the charge carriers (negative electrons and positive halls), about the concentration of the free charges n or p and about their mobility ?. About the Hall effect, “harmonious” and as though experimentally concurring theory is developed, which have been working successfully in the solid electronics and sensorics for more than 60 years. Moreover, in 1980, this theory was enriched by the exceptionally important quantum Hall effect, discovered by the Nobel laureate Klaus von Klitzing. The milestone in the classical Hall effect theory is the Lorentz force FL deflecting laterally the moving charge carriers.
The Lorentz force FL always presents in materials carrying an electric current IS and exposed to a perpendicular magnetic field B. The Lorentz force’s contribution to the modern civilization is immense, as it is in the basis of all electro-motors, generators, sound-reproducing systems, measurement modules, etc. The Lorentz force FL deflects to the corresponding boundary surface the charge carriers and on the opposite boundary of the material structure non-moving (static) charges appear. The electrical field EH generated by such charges compensates the deflecting action of the Lorentz force FL, -eEH = FL. Namely the electrical field EH generates the Hall voltage VH.
But the authors did not agree completely with such formulation of the Hall effect theory as settled static electrical charges in the both boundaries of the structure. Almost all of the materials with finite dimensions are similar to capacitors! This sounds absurdly and non-seriously. For long time, our resignation has been keeping by the fact that such theory “has been working”. It seems to be paradoxically, but we were not troubled to assert that we did not understand the Hall effect interpretation very well.
At one moment, we decided to forget about the “harmonious” model of the Hall effect. Our reasoning was approximately as follows: the electrical charges concentrated into one of the sample boundaries by the Lorentz force FL must not be immobile. They equally in rights participated in the charge transport process with the other charges in sample volume, increasing the conductivity in the sample boundary, as their concentration there is increased in magnetic field. The concentration of mobile current charges in the opposite boundary of the sample decreased and corresponding conductivity decreased respectively. At stationary conditions, in magnetic field ?, the density of the current Is flowing into one of the boundaries increased but into opposite boundary decreased. Therefore, together with Hall voltage VH, the surface current Im should change in magnetic field ?. Such change should be alternative and independent manifestation of the Lorentz force FL. We developed proper model related to existence of such magneto inducted change of the surface current Im. The most impressing in this saga was the experiment.
In fig. 1, the experimental benchmark used for the registration of the novel magneto-sensitive effect, is shown. On the upper surface of a silicone plate, four ohmic contacts are formed – two outer ?1 and ?2, and two inner ?3 and ?4. Through the contacts ?1 and ?2, the supply current Is = IC1,2 is switched. The innovation is that the both inner contacts ?3 ? ?4 are connected to a measurement device for current. In practice, this was realized by connecting to point ?3 and point ?4 low-resistance etalon resistor R0, which value was considerably lower by comparison with the resistance RC3,4 between contacts ?3 and ?4, R0 < RC3,4. The resistor R0 shunted the boundary zone lC3,4 and this way, the magneto-induced surface current Im, formed in the zones lC1,3 and lC4,2, flow trough the measurement circuit. The external magnetic field ? was applied perpendicularly to the vertical section of the material structure. The samples were realized by means of standard planar technology. The resistivity of the silicone plates were ? ~ 7.5 ? cm; the deepness of the ohmic contacts ?1, ?2, ?3 and ?4 was about 1 ?. Some of the experiments were realized in room temperature ? = 300 K, other of them were realized in cryogenic temperature ? = 77 K. The research was carried out in the Magnetic measurements laboratory of the Institute of System Engineering and Robotics.
In fig. 2, 3 and 4, the typical dependences of the measured between inner contacts ?3 and ?4 signal IC3,4(B)?Im on the external magnetic ? are shown. Generating in the structures of changes in the surface current in magnetic field Im(B) was registered in all of the experiments when Is?0. The new effect exists in wide temperature interval 300 K?T?77 K. As is evident from the obtained experimental results, it manifests the following important feature: linear dependence on supply current Is and induction ?, analogically to the Hall phenomenon. It is necessary to point out that simultaneously with existence of the current Im(B), on both of the contacts ?3 and ?4, a voltage VH was generated due to existence of the well-known parallel-field Hall effect. Such voltage may be measured using Lozanova’s method. Therefore the current Im(B) is independent on the classical VH. But both of the effects were caused by the Lorentz force and due to this reason they manifested related features regarding input parameters B and Is.
The experimentally proved magneto-sensitive phenomenon in materials (in our case, semiconductors are considered) plays the same part as the goal of Hall Effect did many years ago. A practical applicability of the new galvanomagnetic phenomenon is in the field of investigating of the quality of surface of material structures. From here, very important conclusions may be formulated. Do not forget that the interface, Si-SiO2 for example, is rather electronic element with unique properties, but not usual physical limit. In our opinion, the new phenomenon is applicable in micro- and nano structures. The quantum format of the new phenomenon is of interest.