Shubhra Karmakar - Western Michigan University



Future of Computation with Electronic Nanotechnology

(Presented by:- Shubhra Karmakar)

Q # 1:- Explain Moore’s Law with respect to

• Mechanical Relays

• Transistors

• CMOS

Answer

[pic]

As can be seen the number of operations per seconds in Mechanical Relays doubled every 8 years during the early stages of device development.

Interestingly, the same capability of transistors has been doubling every 2 years and for CMOS every 1 year. In order to keep up with this pace of development in operational efficiency, it is predicted that by the year 2030, nanoelectronic devices OPS/sec capability will double every few months

Q # 2:- What are the two paths to nano-electronic devices?

There are going to be two prime paths to nanoelectronic devices.

1. The first path is to develop nano-scale descendents of present day solid-state devices.

2. The second path considered to be more radical, is to fabricate nano-devices from molecules. The second approach is called “Molecular Electronics Approach”

Path-1

Over the last few decades computer power has grown at an amazing rate, doubling every couple of years. This increase is essentially due to the continual miniaturization of the computer's most elementary component, the transistor. As transistors became smaller more could be integrated into a single microchip, and so the computational power increased. However this miniaturization process is now reaching a limit, a quantum threshold below which transistors will cease to function. Present ‘state-of-the-art’ components possess features only a few hundreds of nanometers across (a nanometer is a thousandth of a micron, or a billionth of a meter).

Depicted below is the first technique to get nano-electronic devises

[pic]

|The transition from micro technology to Nanotechnology. The structure on the right is a single-electron transistor |

|(SET), which was carved by the tip of a scanning tunneling microscope (STM). According to classical physics, there |

|is no way that electrons can get from the 'source' to the 'drain', because of the two barrier walls either side of |

|the 'island'. But the structure is so small that quantum effects occur, and electrons can, under certain |

|circumstances, tunnel .through the barriers (but only one electron at a time can do this!). Thus the SET wouldn't |

|work without quantum mechanics. |

Path-2

The second path considered to be more radical, is to fabricate nano-devices from molecules. The second approach is called “Molecular Electronics Approach”

Molecular electronics uses covalently bonded molecules to act as devices. Molecules by virtue of their size are natural nano-scale structures. Molecular electronics will bring the ultimate revolution in computing as: -

a. 1 trillion such devices can be packed into a single chip

b. And the memory capacity in a terabyte level

Also because of their small size, the primary advantage of molecular devices is that they can be fabricated in large numbers. The present day challenge however is to develop methods to incorporate these devices in circuits

Depicted below is the second technique to get nano-electronic devises

[pic]

|From an SET (on the left) to the ultimate computer element: a molecule! Although both these structures use quantum |

|mechanics, only the one on the right could be employed in a true 'quantum computer'. |

Q # 3:- Three disadvantages of scaling down of CMOS ?

As we all know, the current VLSI systems relies heavily on CMOS technology and with miniaturization, it is predicted that by the year 2012, a CMOS will have 1010 transistors.

Consequently, the operating speed will surge to 10-15 GHz.

The path to scale down nano-CMOS is not going to be an easy one.

1 As we scale down devices will become

a. More variable and faulty

1. Also fabrication will become

a. More expensive

b. Constrained

2. The design is also expected to become

a. Complicated

b. Expensive

[pic]

Q # 4:- What are Resonating Tunneling Diodes (RTD’s) ?

Resonant-tunneling devices

Here, we focus primarily on explaining the operation of resonant tunneling devices, because they employ quantum effects in their simplest form [1]. Presently, these devices usually are fabricated from layers of two different III/V semiconductor alloys, such as the pair GaAs and AlAs. The simplest type of resonant tunneling device is the resonant tunneling diode (RTD). As depicted in Figure 2(a), a resonant-tunneling diode is

made by placing two insulating barriers in a semiconductor, creating between them an island or potential well where electrons can reside. Resonating tunneling diodes are made with center islands approximately 10 nanometers in width. Whenever electrons are confined between two such closely spaced barriers, quantum mechanics restricts their energies to one of a finite number of discrete "quantized" levels. This energy quantization is the basis for the operation of the resonant-tunneling diode. The only way for electrons to pass through the device is to However, when the energy of the incoming electrons aligns with that of one of the internal energy levels, as shown in Figure 2(c), the energy of the electrons outside the well is said to be "in resonance" with the allowed energy inside the well. Then, current flows through the device--i.e., the device is switched "on." By adding a small gate electrode over the island of an RTD one may construct a somewhat more complex resonant tunneling device called a resonant tunneling transistor (RTT). In this three-terminal configuration, a small gate voltage can control a large current across the device. Because a very small voltage to the gate can result in a relatively large current and voltage across the device, amplification or "gain" is achieved. Thus, an RTT can perform as both switch and amplifier, just like the conventional bulk-effect transistor. Unlike conventional bulk effect transistors, which usually have only two, switching states, "on" and "off," resonant tunneling devices like RTDs and RTTs can have several switching states.

[pic]

Q # 5:- Disadvantages and Advantages of Resonating Tunneling Diodes (RTD’s)

1. The advantages of RTDs are

a. Multiple logic stages are possible

b. These are semiconductors based devices capable of large scale fabrications

2. The same scaling limitations (disadvantages) as CMOS exist.

These devices are currently in production

Q # 6:- What are Spintronics and what is it based on? Give 2 devices based on Spintronics?

The terms Spintronics, Spin-Electronics and Magneto-Electronics are synonymous. IBM commercialized this concept in 1997, which uses the spin of electrons rather than charge to store information. Information is stored into spins as a particular spin orientation (either UP or DOWN).

All Spintronic devices act according to the simple scheme: (1) information is stored (written) into spins as a particular spin orientation (up or down), (2) the spins, being attached to mobile electrons, carry the information along a wire, and (3) the information is read at a terminal. Spin orientation of conduction electrons survives for a relatively long time (nanoseconds, compared to tens of femtoseconds during which electron momentum decays), which makes Spintronic devices particularly attractive for memory storage and magnetic sensors applications.

Two devices based on Spintronics:-

• MRAM

• MCPU

Magnetic RAM is a more imminent development than a magnetic CPU, because CPUs involve more complex hardware.

Magnetic Random Access Memory:-

An obvious application is a magnetic version of a random access memory (RAM) device of the kind used in your computer. The advantage of magnetic random access memory (MRAM) is that it is 'non-volatile' - information isn't lost when the system is switched off. MRAM devices would be smaller, faster, cheaper, use less power and would be much more robust in extreme conditions such as high temperature, or high-level radiation or interference.

Magnetic Central Processing Unit:-

In the distant future, programmable magnetic logic elements could be configured to form magnetic central processing units (MCPUs) — the brains of the computer. An MCPU could be reprogrammed on the fly so that the architecture of the machine optimally matches the subtask at hand.

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Thus, as the voltage bias on an RTD is increased from zero, where it is "off," the device initially switches "on" when the first energy level comes in resonance with the

incident electrons. Then, it switches off again as the bias is increased further, past resonance. However, if there is a second energy level in the quantum well, then the device

can switch on again as the bias voltage of the RTD (or the gate voltage of an RTT) is increased still further. This multistate switching behavior permits each device to

"count higher" and represent more logic states.

Graph:- This is a Reliability curve which shows the probability of failure versus number of operating years. There is a 50% failure rate after a period of 5 years.

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