Information processing structures

Details Information processing structures Information processing structures

2001-12-04

2003-12-09

Pham, Long (Department: 2814)

Active solid-state devices (e.g., transistors, solid-state diode

Thin active physical layer which is

Heterojunction

C257S023000, C326S036000

Reexamination Certificate

active

06661022

ABSTRACT:

TECHNICAL FIELD
The present invention relates to an information processing structure for processing information by means of an electronic structure of a nanometer (nm) scale, for example from 10 nm to 0.3 nm and in particular to an information processing structure for detecting similarity of one pattern to another by way of single electron operations.
BACKGROUND ART
The progress of microelectronics techniques for semiconductors in recent years has come to make it possible to manufacture a structure of the so-called nanometer (nm) scale, for example 10 nm or less. Utilizing such a microelectronics technique to fabricate a structure extremely small in electrostatic capacitance makes the so-called Coulomb blockade phenomenon observable that a single electron in the structure has its electrostatic energy so increased that no other electron can come into the structure. And it also makes movement of an individual electron controllable by Coulomb repulsion between them.
It is thus possible to make a small conductor (microconductor or small semiconductor (microsemiconductor)) domain in which an electron can be extant (hereinafter referred to as a “quantum dot”) by combining an energy barrier that the electron can directly tunnel (hereinafter referred to as a “tunnel junction”) and a coupling with which the electron cannot directly tunnel the barrier hereinafter referred to as a “capacitive coupling”), and then to form an electronic structure by combining such quantum dots. As is well known, such quantum dots can be formed by the self-assembling formation in which silicon quantum dots are formed by low pressure CVD using mono-silane (see Mat. Res. Soc. Symp. Proc. 452 (1997) 243 “Self-Assembling Formation of Silicon Quantum Dots by Low Pressure Chemical Vapor Deposition”).
An electronic device when formed of such an electronic structure becomes to be operable by movement of a single electron. Such an electronic device is commonly called a single electron device, and a variety of single electron circuits have been proposed by taking advantage of single electron devices. For example, it is possible to form as an electronic device a complementary transistor akin to a CMOSFET, and a single electron logic circuit using such a complementary transistor has already been proposed (See J. Appl. Phys., Vol. 72, No. 9, 1992, pp. 4399-4413, J. R. Tucker: “Complementary Digital Logic Based on the Coulomb Blockade”).
Such proposals made for a single electron logic circuit, however, have so far not gone beyond only its circuit makeup by combining a tunnel junction and a capacitor on the circuit diagram level, and has scarcely as yet been implemented as a practical form, namely as an actual structure of the circuit.
Also, as regards a memory, while a “quantum dot floating gate memory structure” which it is designed to form by microstructuring the conventional floating gate structure has been proposed and made by way of trial, no practical form of implementation or no actual structure of the circuit has as yet been proposed that effectuates logics for information processing.
By the way, there is one important form of information processing operations that detects similarity of one pattern to another. This is a basic processing operation that can be utilized in a wide range of information processing including pattern recognition for associative memory, vector quantization and prediction of a movement and data compression.
In such processing operations, use may be made of a “Hamming distance” as an index to indicate similarity between digital patterns. This is defined by the number of those bits differing from each other of the digital patterns. Thus, it follows that the smaller the difference in the number of such different bits, the smaller the Hamming distance and the higher the similarity between the patterns, viz. more closely the patterns resemble each other. Here, the Hamming distance can be computed, for example, by finding the exclusive ORs (XORs) of corresponding pairs of bits of the two digital patterns and summing those with the 1 output.
By the way, a circuit as shown in FIG.
14
(A) having a capacitor C
0
combined with a single electron transistor (hereinafter referred to as “SET”) made up of a pair of tunnel junctions
1
and
2
exhibits a non-monotone characteristic as presented by the aforementioned Coulomb blockade phenomenon (See Applied Physics [a Japanese journal], Vol. 66, No. 2(1997), p. 100) and therefore, if supplied with voltages Va and Vb via capacitors at an intermediate point between the two tunnel junction
1
and
2
, namely at its isolated node
3
, exhibits a change with time dependence of its output voltage Vco as shown in FIG.
14
(B) depending on a combination in H or L level of the input voltages Va and Vb. Utilizing such a characteristic, there has been proposed a single electron logic circuit designed to provide an XNOR (exclusive NOR or inhibit exclusive OR) gate by combining a single SET with a capacitor C
0
(See “A Stochastic Associative Memory Using Single Electron Devices and Its Application to Digit Pattern Association”, T. Yamanaka et al, in Ext. Abs. of Int. Conf. on Solid State Devices and Materials, pp. 190-191, Hiroshima, September 1998).
FIG. 15
shows a further single electron logic circuit in which a pair of SETs is connected parallel to each other between a power supply Vdd and a capacitor C
0
and to which inverted voltages of Va and Vb are also applied, thus providing a complementary structure. Such single electron logic circuits may be prepared in number equal to the number of bits of digital patterns to be compared with each other and may be connected to a common capacitor (C
0
) to make up a bit comparator (BC) for the digital patterns as shown in
FIG. 16
in which Va represents a bit voltage of one digital pattern to be compared and Vb represents a bit voltage of the other digital pattern to compare with. Then in the SETs in which their respective bits coincide with each other (Va=Vb), the electron moves from the capacitor C
0
to the power supply Vdd, raising the potential at the capacitor C
0
as shown in FIG.
15
(B). It follows therefore that the greater the number of bits coincident with each other, the more rapidly the capacitor potential Vc
0
rises. Therefore, examining a transient change in the potential rise permits the size of the relative Hamming distance to be known. A bit comparator for digital patterns of such a construction has already been proposed.
Also, given the fact that a circuit formed of single electron devices operates stochastically, it has previously been known that conversely utilizing this stochastic nature makes it possible to realize an intelligent processing operation which it has been hard to realize in an existing CMOS circuit (See Yamanaka et al, 1998 supra; and IEICE Tramn. Electron., Vol. E81-C. No. 1, pp. 30-35, 1998, M. Saen et al, “A Stochastic Associative Memory Using Single Electron Devices”).
No such single electron logic circuit has as yet been proposed, however, as to in what structure it may actually be implemented.
Also, the problem has existed that because as the time elapses the electric potential V
co
of the capacitor C
0
becomes constant without depending on the Hamming distance, the Hamming distance cannot be measured in a stable state.
Further, making a single electron logic circuit by applying the existing architecture of a CMOS logic circuit thereto involves theoretically fatal problems as mentioned below.
First, the fact that the tunneling phenomenon on the basis of which a single electron circuit operates is stochastic requires it to take fairly long before its operation is established, and makes the operation slow. Thus, the single electron logic circuit made by applying the architecture of a CMOS logic circuit must be slower in operation than, and hence fail to be superior to, the conventional CMOS logic circuit.
Second, no stable single electron operation can be obtained unless the electrostatic energy of one electron is enough larger than its thermal energy. This

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