  We propose a novel concept of obtaining oscillations with frequencies in
very-high frequency (VHF) and ultra-high frequency (UHF) bands. A traditional
spin torque nano-oscillator (STNO) consists of at least one pinned layer (PL)
and one free layer (FL) which precesses in a fixed orbit, defined by a
precession angle, which results in magneto-resistance (MR) oscillations. In
STNO, with aligned or even orthogonal easy-axis of the magnetic layers and with
or without external bias magnetic field, it is not possible to attain full MR
swing. The constringed MR swing jeopardizes the extracted output power.
Furthermore, the orbit is strongly disturbed by the thermal fluctuations
resulting in strong magnetic noise. In stark contrast to the operation
principle of a STNO, we theoretically demonstrate, with the practical
parameters from the experiments, that with a unidirectional current in a dual
asymmetric free-layers (with no pinned layer) based perpendicular magnetic
tunnel junction (pMTJ), both of the free layers can attain a complete and
out-of-phase self-sustained switching without the aid of any external magnetic
field. This design facilitates a switching based spin torque oscillator
(SW-STO) with a full MR swing, and hence a larger output power, for stable and
more thermally robust free-running oscillations. Furthermore, the integration
with the n-type metal-oxide-semiconductor (NMOS) field-effect transistors at
130, 65 and 14 nm node is appraised to expound its effect on the oscillator
performance, controllability with DC bias and the design constraints, to
demonstrate the viability of the design as a dynamically controllable
oscillator for practical on-chip implementation.
