SPIN-WAVE ARCHITECTURES - Bio-Inspired and Nanoscale Integrated Computing - page 205

these proposed modules is relatively low, and the classical type of computing, as
opposed to quantum, is employed. By using phase logic, simple operations such as
AND/OR/NOT can be performed efficiently on the transmitted waves. Signal
detection is accomplished by the time-resolved inductive voltage measurement
technique. In this structure, the sphere of interactions is limited by the spin-wave
attenuation length; therefore, it is suitable to be used as nanoscale computing
modules that can be ported or integrated onto higher-scale chips or devices.
The architecture described here, while requiring the same number of switches
as a standard crossbar, is capable of simultaneously transmitting N waves on each
of the spin-wave paths. As compared to the known molecular crossbars, this
design is fault tolerant: In case there is a failure in one of the N channels, any of
the other channels can be reconfigured to transmit the data. This is possible since
all the channels are accessible by all the ports and each channel can handle
multiple data.
Crossbars are attractive architectures because they can realize any permuta-
tions of N inputs to N outputs. However, their main shortcoming is due to the fact
that N 2 switches are used to transmit only N pairs of data. As mentioned earlier,
each spin-wave bus is capable of carrying multiple waves at any point of time.
Therefore, each of the N inputs can broadcast its data to all of the N outputs in
parallel. Using this type of architecture, it would be possible to efficiently realize
highly connected types of computations such as the Hopfield Neural Network
model, as shown in [9]. An example of the proposed spin-wave crossbar
architecture is shown in Figure 7.2. A set of column spin-wave buses on the
bottom and a set of row spin-wave buses on the top are connected via the vertical
spin wave switches.
An important element required for the spin-wave crossbar is the spin-wave
switch. We define a spin-wave switch as a device that has an externally
controllable magnetic phase. In the ''On'' state, the switch transmits spin waves;

Spin-wave crossbar architecture

V I + 1

V I

V I − 1

Insulator

F(V I ,V I )

p-dopedDMS

Insulator

V I − 1 V I + 1

V I V I + 2

Figure 7.2. Spin-wave crossbar architecture.