335 Alternate Device Structures for CMOS

It is widely recognized that CMOS device fabrication in the sub-50 nm regime will put significant pressure on current device designs and fabrication approaches. Several designs for advanced structures have been proposed, and some have promising capabilities and potential to be manufacturable.18-22 Some of these structures include dual-gate designs, where gate electrodes on top and bottom of the FIGURE 3.5 Schematic diagram of an example vertical field-effect transistor. For this device, the...

7511 Molecular AND and OR Gates Using Diode Diode Logic

Circuits for AND and OR digital logic gates based upon diodes, so-called diode-diode logic structures, have been known for decades. Schematic diagrams for these two circuits are shown, respectively, in Figures 7.12(a) and 7.13(a).106,107 The operation of these logic circuits is explained in Appendix B, Sections B.1 and B.2. Part (b) of each of these figures shows a structure for a corresponding novel molecular implementation of each of these logic gates. It is noteworthy that these molecular...

Miniaturization by Evaporation

How can we make such a device What kind of manufacturing processes would we use One possibility we might consider, since we have talked about writing by putting atoms down in a certain arrangement, would be to evaporate the material, then evaporate the insulator next to it. Then, for the next layer, evaporate another position of a wire, another insulator, and so on. So, you simply evaporate until you have a block of stuff which has the elements coils and condensers, transistors and so on of...

321 Two Terminal Diode and Negative Differential Resistance Devices

The most simple silicon-based solid-state electronic device is the p n junction diode, where the current through the two terminals is small in the reverse direction and depends exponentially on the applied voltage in the forward direction. Such devices have wide-ranging applications as rectifiers and can be used to fabricate memory and simple logic gates.8,9 A variation on the p n diode is a resonant tunneling diode (RTD) where well-defined quantum states give rise to negative differential...

113 Modeling of Quantum Dots and Artificial Atoms

The quantum dot is, in a way, the prototype of any future device that is designed to occupy a minimum of space. It is important in this context that quantum dots can be arranged and intercon nected in three dimensions, at least in principle. In the last 10 years, the physics of quantum dots h as experienced considerable development because of the manifestation of the discreteness of the electron charge in single-electron charging devices, as well as the analogy between three-dimensionally...

1131 The Many Body Hamiltonian of Artificial Atoms

The electronic spectrum of N-electron quantum dots are computed by considering the many-body Hamiltonian where H0i is the single-particle Hamiltonian of the ith electron and is the interaction Hamiltonian describing the Coulomb interaction between carriers. Here is the dielectric constant of the material. In the second term of Equation (11.1), the sum is carried out for i j, avoiding the interaction of carriers with themselves. Quite generally, the Hamiltonian Equation (11.1) is used for...

1332 Nanoscale Contacts Momentum Conservation across a Lattice Plane Contact

The lattice plays a critical role in the transport of electrons across an interface. The ability to control the registry angle between the nanotube and the graphite substrate provides us the opportunity to study the electron transport dependence on the orientation of the crystalline axis in the contact. We have measured the resistance of the CNT graphite contact via a two-probe measurement the graphite substrate itself serving as one lead, and a conducting AFM tip brought to contact the top of...

106Molecular Junction Conductance and Nonadiabatic Electron Transfer

Electron transfer is one of the most important areas of chemical kinetics, biochemical function, materials chemistry, and chemical science in general.106-107 In electron transfer reactions, electronic charge is moved either from one molecular center to another or from one section of a molecule to another section of that FIGURE 10.7 The effective tunneling barrier for an electron passing through a rectangular barrier in the potential. The modifications in height are due to interactions between...

97 Quantum Grid Infrared Photodetectors

In the previous sections we discussed the QWIP properties pertaining to the nanometer scale of the material thickness. In this section, we describe an attempt to create lateral quantum confinement within the material layers. This approach employs electron-beam lithographic techniques to generate desirable two-dimensional patterns on the QWIP material surface.42,43 The detector material is then etched down to the bottom contact layer by low-damage reactive ion beam etching (RIBE).44 Some...

932 Multiple Quantum Wells

We apply the calculation to several common detector structures.16 Figure 9.3 shows the band diagrams and the relevant energy values of three detectors. Because barriers are thick, the ground state wave functions are localized. The structures are referred to as multiple quantum well (MQW) structures. Detectors A, B, and C are respectively bound-to-bound, bound-to-continuum, and bound-to-quasi-bound detectors. In the actual experiment, each detector consists of 20 QW periods. But we apply the...

References

S.Wolf et al., Spintronics a spin-based electronics vision for the future. Science. 294, 1488 (2001). 2. G. Prinz, Magnetoelectronics. Science. 282, 1660 (1998). 3. G. Prinz, Magnetoelectronics applications. J. Magn. Magn. Mater. 200, 57 (1999). 4. H. Ohno, F. Matsukura, and Y. Ohno, Semiconductor spin electronics. JSAP Intl. 5, 4 (2002). 5. M. Freeman and B.C. Choi, Advances in magnetic microscopy. Science. 294, 1484 (2001). 6. M. Baibich et al., Giant magnetoresistance of (001)Fe (001)Cr...

69 Some Problems in Nanocomputer Hardware Software Modeling

In this section we will discuss the mathematical model development issues. While the importance of mathematical models in analysis, simulation, design, optimization, and verification is evident, some other meaningful aspects should be emphasized. For example, hardware and software codesign, integration, and verification are important problems to be addressed. However, these problems interact with mathematical modeling and analysis. The synthesis of concurrent nanocomputer architectures...

1123 Tunneling in Ultra Thin Oxides

The thickness of gate oxides in MOSFETs is approaching 1-2 nm, i.e., only a few Si-O bond lengths. Consequently, gate leakage currents have become a major design consideration. For such ultra thin oxides, it is increasingly important to understand the influence of microscopic structure and composition of the oxide and its interface with silicon on the magnitude of oxide transmission probabilities and tunneling currents. To fully explore the microscopic nature of gate le akage currents, an...

125 An Example Quantum Point Contact QPC

Consider, for example, a gold wire stretched between two gold surfaces as shown in Figure 12.18. One of the seminal results of mesoscopic physics is that such a wire has a quantized conductance equal to e2 FIGURE 12.18 Left, wire consisting of six gold atoms forming a Quantum Point Contact QPC . Right, quantized conductance I e2 nh V . nh 77.5 A V 12.9 kD -1. This was first established using semiconductor structures29,40,41 at 4 K, but recent experiments on gold contacts have demonstrated it at...

124 Nonequilibrium Greens Function NEGF Formalism

The one-level toy model described in the last section includes the three basic factors that i nfluence molecular conduction, namely, Ef - 0, r12, and U. However, real molecules typically have multiple levels that often broaden and overlap in energy. Note that the two-level model Figure 12.12 in the last section treated the two levels as independent, and such models can be used only if the levels do not overlap. In general, we need a formalism that can do justice to multiple levels with...