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Nanotechnology is a study of materials sciences of the size in the range equal to that of atoms and molecules. It is now becoming a diversified field as it is used in the analysis of the areas relating conventional physics up to the areas consulting with self assembly with the nano scale dimensions. The development of the standard devices at the nanometer scale with the potential of large scale integration and room temperature operation was a difficult task. Over the passage of time many newly developed technologies have been proposed on the basis of highly qualitative reasoning or by the simplified physical models. The problems arise to cause the nanodevices may be due to insufficient maturity of the available technology.
As it is known that for the field relating design and manufacture CAD/CAM tools provide much of motivation is the successful development of the product, it is also used in the integration with the nanotechnology. This integration with nanotechnology is clearly visible by the use of new technologies that have been developed. This report includes some of the new technologies such as NANOTCAD and NANO scaling of self assembly.
Road to NANOTCAD....................................................................................6
Application of NANOTCAD.....................................................................8
CAD/CAM for nanoscale self assembly-based non robot.......................9
Implementation and experimental procedure.........................................11
Discussion of future prospects....................................................................13
Nanotechnology is a field of science which analyses any given matter in terms of atoms and molecules in the range of the size 100 nanometres or smaller. Nanotechnology is a diverse field which deals with the conventional device physics to the recent approaches based on molecular self assembly with the nanoscale dimensions. Nanotechnology has its advantage with the potential to design and develop many devices with a wide range of applications such as medicine, electronics and energy production.
Computer-aided design and manufacture (CAD/CAM) has been a major area of application for computer graphics and computational geometry, and has provided much of the motivation for the field of geometric modelling. The link between design and manufacturing is generally recognized as important, but it depends strongly on the manufacturing processes to be used. Much has been developed about CAD/CAM for machining and other traditional manufacturing processes.  Nanotechnology had made a greater impact in the revolution of CAD and CAM in the field of electronics. Development of CAD at circuit, logic and architectural levels provide a valuable feed back to nanotechnology for the development of new nano devices.
NANOTCAD aims to play the same role in the development of nanoelectronic to that which existing CAD tools have played in the successful development of each new generation of microelectronic circuits and devices. NANOTCAD has successfully developed a computer-aided design (CAD) system to make the creation of nanoelectronic devices easier and more cost and time-efficient. It also developed nano devices to test its CAD system, and these too are state-of-the-art in their own right. Among them are two techniques to fabricate a molecular device in which a small molecule bridges two metal electrodes separated by a gap of one nanometre. NANOTCAD designed two systems to check for the functionality of the CAD systems.
An enhanced prototype of the flash memory based on quantum dots
Unique signature that allows ballistic transport in field-effect transistors
(Ballistic field effect transistors are identified to accelerate the operating speeds and avoid power loss in micro nano chips.)
This software newly developed with CAD used technology is useful in order to predict the advantages and disadvantages that may arise during the development stages of nano-electronics devices. As the devices developed by the software package show, NANOTCAD's one, two and three dimensional design programmes have met this goal - an objective that is especially significant given forecasts for the future of the field.
Road to NANOTCAD
The design and development of the novel devices at the nano scale with the possible large scale integration and optimal operation was an impossible task to perform. Over the years, many ideas have been proposed on the basis of very qualitative reasoning or simplified physical models: typically, the demonstration of working prototypes is achieved, while the fabrication of complex logic circuits proves to be unfeasible. In some cases there was an undesirable outcome which was mainly due to fundamental problems. Nanotechnology strongly relies up on the computer aided design tools for its industrial and economic development in the same way as microelectronics relies on TCAD. Hence with a broader area of knowledge of the CAD tools for nanotechnology, a real and competitive advantage with the significant impact in terms of economic development was attained.
NANOTCAD tools were developed for the research and prototyping and to find a solution for some of the above mentioned problems with advanced usage to solve the difficulties of nanoelectronic and molecular electronics and in detail solving the problems arise due to modelling tools of realistic devices and structures. This same tool was also used in the design of various other robust devices and structures with the potential for the use in large scale integration.
The development of NANOTCAD consists of six divisions: four of them are directly involved in the theoretical activity of model and code development, and other two are involved in the fabrication and characterization of state-of-the-art nanoscale devices and structures.
The objectives of the development of NANOTCAD included:
Development and validation of a hierarchical set of software tools for the simulation and the design of a wide spectrum of devices, based on semiconductors and on transport through single molecules.
The set of tools developed with NANOTCAD aims in usage at device prototyping and early evaluation of the device structure. NANOTCAD also is used in solving the self-sufficient Schrödinger -Poisson equation in three dimensions in semiconductor structures, for open and closed systems, to compute for the densities of the atoms and molecules attached to the conductions electrodes in order to stimulate the transportation of molecular electron devices and hence to compute the I-V characteristics both in linear response region and a state away from equilibrium. In addition to this it allows to model nanoscale structures coupled with conventional electronic devices and to determine the behaviour of the temperature from 0K to room temperature. This could be attained with a significant progress in the modelling the quantum transport in the realistic nanoscale devices in the whole range of transport regimes. NANOTCAD package was hence developed with aim to address the border possible range of the nanotechnology devices and freely available to the nanotechnology community.
Demonstration of a procedure for the realization of prototypes of nanoscale devices based on detailed modelling.
The major importance for developing such software is to provide an accurate step by step procedure primarily to detect the design flaws in the early stages of candidate device structures and thereby evaluating and solving the respective problem by designing a optimised design structure simulations. Hence this procedure allows more efficient and quicker design prototyping. This procedure was designed, verified, applied and refined through the realization of two different prototype classes of the nanoscale devices which are the other two objectives of the proposal which are:
Design, fabrication, characterization and optimization of single and double quantum-dot HFETs for use as single /few electron memories, and resonant tunnelling diodes, and nanoscale HFETs.
The design, fabrication, characterization and optimization of devices in which transport occurs via one/few molecules connected to metal electrodes.
As mentioned earlier the three programs have been developed for the simulation of semiconductor nanostructures in quasi-equilibrium conditions in one-, two-, and three-dimensional domains such as NANOTCAD1D, NANOTCAD2D, NANOTCAD3D, respectively. All codes are based on the solution of the many-body Schrödinger equation with density functional theory, local density approximation, and allow subdivide the domain in several regions with different types of quantum confinement, providing a reasonable level of flexibility. In addition, NANOTCAD2D also allows stimulating ballistic FET both in the III-V and in the Si-SiO2 material system.
One dimensional simulation may be performed with the Poisson-Schrödinger (PS) solver NANOTCAD1D and with the quantum Monte Carlo code VMC (Vienna Monte Carlo). NANOTCAD1D computes the self-consistent potential, charge density profiles, and the current through one or more barrier layers. VMC reads the potential profile from the PS solver and computes the terminal current and distributed quantities such as charge density, mean energy, and mean velocity, by taking into account phonon scattering. Typical run time of NANOTCAD1D is in the order of few minutes, while the much more physically detailed VMC has simulation times ranging from hours to a few days.
Two dimensional simulations of the Poisson-Schrödinger equation and of the continuity equation for the ballistic current in 2 dimensions can be performed with NANOTCAD2D. It can be used for the simulation of quantum wires and of ballistic field effect transistors.
Available tools for the three-dimensional simulations of semiconductor structures are NANOTCAD3D, which is available to the general public through the PHANTOMS hub, and SIMNAD, that will be made freely available to institutions with a license of the ISE-TCAD package. NANOTCAD3D is a 3D Poisson-Schrödinger solver, in which several regions with different degrees of confinement can be defined, and structures described in the present and the preceding report can be simulated (QD memories, SETs, FETs, etc..). SIMNAD is a 3D PS solver which can be coupled to a commercial drift-diffusion simulator, and allows simulating devices containing both quantum confined regions (e.g. quantum dots) and regions in which transport is described by the drift-diffusion model. Simulation of transport through a single molecule for a given contact-molecule-contact system is performed with the newly developed VICI program. VICI relies on physical model that can treat electron interaction to an arbitrary accuracy, and goes beyond linear response allowing the investigation of transport in far from equilibrium conditions.
Application of NANOTCAD:
NANOTCAD has a very wide range of application in the field of electronics. Following are the few applications of NANOTCAD:
Used in the designing of MOSFET's and HFET.
MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is a device used to increase or switch on the electric signals. NANOTCAD tools are used in designing the semiconductors devices like gates electrode and body electrode. The CAD tools used here are just prototype tools.
Used in the fabrication of mott-FET's
This method is called as nanofabrication which helps in fabrication of Field Effect Transistors.
Used in developing 3-D simulators for semiconductor devices (SIMNAD).
SIMNAD (Simulator for Nano Devices) this is quantum mechanical 3D simulator for semiconductor devices. SIMNAD can be used in computing the self consistent quantum mechanical charge density in semiconductor nanostructures.
CAD/CAM FOR NANOSCALE SELF ASSEMBLY- BASED NONROBOTICS
The general frame work for nanoscale self assembly using cad is implemented intensively in order to improve the efficiency and accuracy of the atomic force microscopic based nanoassembly. With aid of cad modelling of the nanostructure and nano-objects generates path on the surface of AFM image to manipulation of paths and in turn manipulate the nano-object.
The nanoscale assembly in robotics use the technology of the atomic force microscope for the purpose of nonmanufacturing. As AFM lead to the potential breakthrough in new revolutionary industrial products because many potential nanostructures and nanodevices are asymmetric, this cannot be manufactured using self assembly only. In order to increase the efficiency and accuracy CAD is used for the manufacturing of nanostructures and nanodevices. These implementations are done either manually or by the user machine interface.
Nanoscale materials have unique mechanical, electronic, optical and chemical properties have a wide range of potential applications like Nano Electro Mechanical Systems.
(NEMS) and Nanosensors. The two major techniques used in nanoassembly are "Bottom-up" and "Top-down". Among the above two techniques "bottom-up" is considered as promising and efficient technique, for symmetric pattern of nanoentities. However "bottom- up" techniques in the manufacture of nanostructures are asymmetric by the use of self assembly only. The use of "top-down" technique is used instead.
In the course of nanostructure development there are few problems encountered which are:
Identification of nanoobjects
Design of nanostructure
Automatic generation of manipulation paths and drift compensation.
There are two main stages involved in the development of nanostructures:
Modelling of nanoenvironments
Model of nanostructure using cad
Modelling of nanoenvironments
The nanoobjects exist in the form of nanoparticles and nanorods which are distributed randomly on a surface, its positions have to be determined separately in order to define the manipulation paths. After obtaining the AFM image the nanoobjects are identified and categorised as shown in fig.
The X-Y co ordinates and height information of each pixel can be obtained from the AFM image data. This information is further used as criteria to identify nanoobjects and obstacles based on this method
The information obtained from the AFM image data, a 2-D CAD model is being developed for a nanostructure which comprises of nanoparticles and nanorods using unigraphics is designed. From this designed data the positions of the destinations where the nanoobjects will be manipulated in the nanostructure can be obtained. (Refer fig b)
Implementations and experimental procedure
The experimental procedure is as shown below
It consists of an AFM with peripheral devices including an optical microscope, a multifunction data acquisition card and two computers. The AFM system consists of AFM head single access module and AFM controller. The AFM head system scans the object in the range 90µm Ã- 90µm in the X-Y direction and of the range 5µm in Z direction. The SAM (signal access module) transfers signals among the AFM head. SAM is also connected to the main computer which is responsible for the control program to run and provide an interface for imaging. The two computers communicate through the Ethernet to provide the user a real time nano manipulation.
As we know that the CAD model of a nanostructure and the AFM image of a surface are processed and automated path planner generates initial manipulation paths. Here the nanoobjects are processed one by one. Primarily a local scan is done to identify the position of the nanoobjects. Hence, manipulation path is been adjusted using the actual position. This manipulation also includes nano manipulation. This process is continued until all the nanoobjects are well identified and manipulated to their respective destination. After the nano assembly is done, it is scanned finally to verify the results in the image mode. The developed algorithms are used in order to manipulate nanoparticles and nanorods and then to fabricate nanostructures.
DISCUSSION OF THE FUTURE PROSPECTS OF CAD/CAM IN NANOTECHNOLOGY
The NanoTechnology CAD is one of the few developed methodologies that can reduce development cycles and costs. Device modelling is used for scaling studies and technology optimization; therefore, the ability to correctly represent today's performance and predict tomorrow's limitations is paramount. The latest ROAD map to modelling and simulation devoted to NANOTCAD, and its subsections dealing with the device modelling. Nanotechnology cannot acquire complete industrial and economic relevance until it strongly uses the intelligence of computer aided design tools. This principle is same as microelectronics using TCAD tools. NANOTCAD codes are the tools that are developed particularly for the purpose of research and prototyping. But its development in present day scenario had helped in creating the necessary expertise on which the possible industrially oriented successor NANOTCAD could be based.
Benefits to society
Semiconductors based single-electron nano devices both from III-V materials and from silicon represent a field of growing interest and a challenge in technology development. TCAD (Technology Computer Aided Design) is expected to become an increasingly valuable tool because of the immense difficulties (and costs) in producing nano-scaled devices with well-defined functionality. The following table from the Technology Roadmap for Nanoelectronics shows the expected development for SET (Single Electron Transistor) logic.
~ 1 MHz
Number of electrons
All the codes and terminologies related to NANOTCAD are being fully developed and delivered to the respective areas of usage. As seen from earlier discussions, this tools is not a unique set of tool but a hierarchical set of tools with its own different levels of complexity and accuracy in its use in respective areas as mentioned. This package is made for the broader use to the society as all the codes except SIMNAD are freely available through Phantom simulation hub (www. Phantomhub.com). this software has problem solving capabilities in the mobility improvement of semiconductor devices, mobility degradation of MOSFET's with high K dielectrics and control of phase coherence in semiconductor implementation of quantum computing.
From the detailed report on Nanoscale it is evident that Nanoscale is assumed to be an extension of its macro and micro counterparts. But this assumption may be wrong because the systems described here have very important role to play, in the same time these systems tends to show randomness instead being deterministic and also have some desirable characteristics of biological systems. Still some of the traditional CAD models seem to be appropriate for Nanoscale application. But in the future if we link between CAD/CAM it will be a great boost to the new and emerging manufacturing process. The latest approach used in building objects is independent and this approach is considered to be one of the attractive methods in Nanoscale. The major obstacles we are facing in implementing active self-assembly come from the hardware side.
In order to enhance the efficiency and accuracy of the AFM based Nanoassembly, automated nanoassembly is recommended. This approach of nanoassembly is considered to be very challenging and complicated because the generation of manipulation path of different nanoobjects we also come across to errors due to the random drift and cantilever deformation. Instead of nanoscaling a simple local scaling method can be adopted in order to reduce the errors in manipulation path. Hence in order to enhance and improve the future prospectus of Nanoscaling the errors occurred due to path manipulation has to be minimised. And a general framework for the development of nanostructures has to be developed; also CAD-guided automated nanoassembly for complex nanostructures has to be adopted.
NANOTCAD is modern technology which uses CAD tools as its designing aids NANOTCAD have vast applications in the field of electronics. With the help of NANOTCAD the designing of semiconductors has become easier and fast compared to other designing tools. This tool helps to reduce the product development cycle time and hence cost of involved is reduced. NANOTCAD has wide range of applications in 1D, 2D and 3D designing. NANOTCAD has major application in designing of MOSFETS, HFET and 3D simulators called as SIMNAD
Nanoscaling of self assembly is another aspect of Nanotechnology where CAD/CAM is effectively utilised, nanoscaling self assembly has increased the accuracy in object recognition and efficient path manipulation of nanoobjects. With the help of nanoscaling an experiment has been carried out in order to obtain the imaging mode.
From the above discussed topics it is clear that the CAD/CAM implementation in Nanotechnology has greatly benefited the field of Nanotechnology. Since the present application of CAD/CAM in this field is limited. It is clear that there is further scope for improvement.