Conventional electronic devices are built using inorganic semiconductors, with silicon being the most prominent example. However, there are two major inherent problems that the silicon industry faces, namely that conventional silicon based transistors will be reaching their theoretical limits (in terms of operation speed) within one to two decades, and that conventional inorganic semiconductor based electronics are unsuitable for certain novel applications. Most of the research and development in nanoelectronics seek to address these two issues.
Transistors – the active component of virtually all electronic devices, are what we refer to as electronic switching devices. In a transistor, a small electric current can be used to control the on/off of a larger current. By suitably connecting multiple transistors, Boolean gates can be created, and from these Boolean gates, microprocessors for computers can be built.
Moore's Law predicts that the computation speed of microprocessors doubles every 18 months. This has been achieved in the past 30 years or so primarily by shrinking the sizes of the silicon based transistors in the microprocessors – with reduced sizes, electrons can pass through the components faster, and hence contributing to a much enhanced operating speed. However, the scheme of shrinking conventional transistors cannot go on forever. When the feature sizes of the electronic devices shrink to the nano-meter regime, quantum mechanical effects (such as tunneling) start to take place, and the operations of the devices would break down completely (The Pentium IV microprocessor has its smallest feature size at about 180nm, so it’s getting close to where quantum mechanical effects take over classical bulk-effects). Thus, without radically new designs and architectures to replace electronics designs, Moore’s Law would come to a dead-end in 15 years or so, and this is why there is such a thrust in exploring a new generation of nano-meter scale electronic devices.
Nano-meter scale electronic devices can be roughly divided into two broad classes: molecular electronics and solid-state quantum effect devices. Molecular electronics utilizes individual molecules to serve as the active components of the device (e.g. single molecule transistors), while solid-state quantum effect devices harness quantum mechanical phenomena (the very thing that’s going to break silicon transistors) for its operation.
Some examples of solid-state quantum effect devices include resonant tunneling diodes, single-electron transistors, spintronic devices, quantum dots (quantum cellular automata), carbon nanotube (CNT) electronics and other semiconductor nano-structures. However, most research on these devices is still in infancy, as relatively few research groups in the world have the capabilities and resources to fabricate and study these ultra small devices.
By utilizing quantum phenomena, not only can ultra-small transistors be made, but also a whole new class of electronic devices such as ultra high capacity mass storage devices, and science fiction-like quantum computers. A quantum computer is a device that utilizes the quantum mechanical effect of superposition to create a "qubit" (a quantum mechanical "bit"), and with it, massive parallel computations can be done, out-performing any supercomputer that we have now. However, creating and maintaining a “qubit” remains a formidable task, as decoherence (aka noise) always interferes and destroys the quantum state. Some solid-state quantum computer design schemes have already been proposed by various research groups, and don’t expect to find a bulk-effect silicon transistor inside!
If nano-transistors and quantum computers seem to be too distant into the future, let’s turn to things that are probably closer to reality.
The mainstream semiconductor industry has been mostly concerned with silicon for the past half-a century. However, in recent years, silicon technology has been found to be increasingly inadequate for some novel applications that have been proposed for the (near) future. For instance, some new integrated circuit designs require light-emitting components for optical signal processing; however, light emission from silicon is highly inefficient. On the other hand, other inorganic efficient light-emitting semiconductors are relatively expensive and difficult to process. Inorganic semiconductors are also unsuitable for other new applications such as flexible electronic displays (inorganic semiconductors being brittle and rigid) and printable electronics (from a printer!): we need to look for something new.
If inorganic semiconductors don’t work, what will? Try organic molecules and polymers! Although once thought as insulators, organic materials have come to the spotlight as they are now better understood, and the discovery of more and more organic semiconductors (such as buckyballs, or C60). A lot of organic materials are relatively flexible, cheap to produce, and easy to process. Moreover, molecules and polymers can be designed and synthesized to provide the desired electronic/light emission properties for particular opto-electronic applications. For instance, the molecule Alq3 has been used extensively for fabricating organic light emitting diodes (OLED). Other examples include printable electronic devices, thin-film transistors, carbon nanotube field-emission displays, and organic based solar cells. Most of these applications are based on thin-film techniques, in which the organic material layer is only about 100nm thick. Although some of these devices have already seen partial commercialization (such as Kodak’s OLED digital camera), a lot more still have to be done by innovators/pioneers like you!
Transistors of the Future
Transistors – the active component of virtually all electronic devices, are what we refer to as electronic switching devices. In a transistor, a small electric current can be used to control the on/off of a larger current. By suitably connecting multiple transistors, Boolean gates can be created, and from these Boolean gates, microprocessors for computers can be built.
Moore's Law predicts that the computation speed of microprocessors doubles every 18 months. This has been achieved in the past 30 years or so primarily by shrinking the sizes of the silicon based transistors in the microprocessors – with reduced sizes, electrons can pass through the components faster, and hence contributing to a much enhanced operating speed. However, the scheme of shrinking conventional transistors cannot go on forever. When the feature sizes of the electronic devices shrink to the nano-meter regime, quantum mechanical effects (such as tunneling) start to take place, and the operations of the devices would break down completely (The Pentium IV microprocessor has its smallest feature size at about 180nm, so it’s getting close to where quantum mechanical effects take over classical bulk-effects). Thus, without radically new designs and architectures to replace electronics designs, Moore’s Law would come to a dead-end in 15 years or so, and this is why there is such a thrust in exploring a new generation of nano-meter scale electronic devices.
Nano-meter scale electronic devices can be roughly divided into two broad classes: molecular electronics and solid-state quantum effect devices. Molecular electronics utilizes individual molecules to serve as the active components of the device (e.g. single molecule transistors), while solid-state quantum effect devices harness quantum mechanical phenomena (the very thing that’s going to break silicon transistors) for its operation.
Some examples of solid-state quantum effect devices include resonant tunneling diodes, single-electron transistors, spintronic devices, quantum dots (quantum cellular automata), carbon nanotube (CNT) electronics and other semiconductor nano-structures. However, most research on these devices is still in infancy, as relatively few research groups in the world have the capabilities and resources to fabricate and study these ultra small devices.
Novel Applications
By utilizing quantum phenomena, not only can ultra-small transistors be made, but also a whole new class of electronic devices such as ultra high capacity mass storage devices, and science fiction-like quantum computers. A quantum computer is a device that utilizes the quantum mechanical effect of superposition to create a "qubit" (a quantum mechanical "bit"), and with it, massive parallel computations can be done, out-performing any supercomputer that we have now. However, creating and maintaining a “qubit” remains a formidable task, as decoherence (aka noise) always interferes and destroys the quantum state. Some solid-state quantum computer design schemes have already been proposed by various research groups, and don’t expect to find a bulk-effect silicon transistor inside!
If nano-transistors and quantum computers seem to be too distant into the future, let’s turn to things that are probably closer to reality.
The mainstream semiconductor industry has been mostly concerned with silicon for the past half-a century. However, in recent years, silicon technology has been found to be increasingly inadequate for some novel applications that have been proposed for the (near) future. For instance, some new integrated circuit designs require light-emitting components for optical signal processing; however, light emission from silicon is highly inefficient. On the other hand, other inorganic efficient light-emitting semiconductors are relatively expensive and difficult to process. Inorganic semiconductors are also unsuitable for other new applications such as flexible electronic displays (inorganic semiconductors being brittle and rigid) and printable electronics (from a printer!): we need to look for something new.
If inorganic semiconductors don’t work, what will? Try organic molecules and polymers! Although once thought as insulators, organic materials have come to the spotlight as they are now better understood, and the discovery of more and more organic semiconductors (such as buckyballs, or C60). A lot of organic materials are relatively flexible, cheap to produce, and easy to process. Moreover, molecules and polymers can be designed and synthesized to provide the desired electronic/light emission properties for particular opto-electronic applications. For instance, the molecule Alq3 has been used extensively for fabricating organic light emitting diodes (OLED). Other examples include printable electronic devices, thin-film transistors, carbon nanotube field-emission displays, and organic based solar cells. Most of these applications are based on thin-film techniques, in which the organic material layer is only about 100nm thick. Although some of these devices have already seen partial commercialization (such as Kodak’s OLED digital camera), a lot more still have to be done by innovators/pioneers like you!
