Having recently been demonstrated at frequencies over 1GHz with measured Q's>10,0001-6, MEMS/NEMS resonators
in silicon, SiC and CVD diamond structural materials have great potential for enabling resonant mass sensing down to
zeptogram resolution as well as on-chip high-Q passives needed in wireless communication systems for frequency
generation, translation and filtering. However, the acceptance of such devices for RF applications in present-day
transceivers has been hindered so far by several remaining issues, including: (1) a frequency range lower than 5 GHz, (2)
higher motional impedances than normally exhibited by macroscopic high-Q resonators, (3) limited linearity and power
handling ability, and (4) insufficient frequency repeatability and stability. This paper reviews several material-centric
strategies for alleviating the aforementioned issues. Given that resonance frequency is generally proportional to the
acoustic velocity while energy dissipation and Q is also a strong function of the material properties, several deviceoriented
and system-level performance-enhancing technologies will be discussed. Both capacitively-transduced and
piezoelectrically-transduced resonators will be discussed with a particular emphasis on the employment of transducers
with improved electromechanical coupling coefficient as the device-level method for lowering the motional impedance.
A metal-insulator-metal (MIM) tunneling diode having response time less than a picosecond (10-12 second) is extremely
important for mixers and detectors operating at terahertz and infrared frequencies. One of the key objectives of this work
is to develop fabrication processes which are well-suited for mass production of nanogap MIM tunneling diodes with
junction area in the range of 10-2 μm2 thus enabling the coveted terahertz frequencies due to the greatly reduced junction
capacitance. A contemporary electron beam stepper of such resolution costs tens of millions and is not viable for mass
production. This work employs standard photolithography and atomic layer deposition (ALD) methods, which allow
formation of a micrometer-wide finger in the second metal layer that is separated from the first layer metal electrode by
an ALD-deposited sidewall dielectric spacer, thus forming a nm-thick vertical tunneling junction. The junction area is
defined by the width of the finger and the thickness of the electrode, while the junction thickness is controlled by the
ALD deposited insulating layer. So far, by using a newly developed process, MIM tunneling diode with micron-scale
self-aligned cross-fingers have been successfully demonstrated. Some preliminary DC characterizations have been
carried out, and device characteristics such as responsivity, I-V, and C-V curves are documented. Ongoing research for
modeling of MIM tunneling diode based on measured data and further reduction of the device junction area enabled by
the new process will lead to MIM diode that could detect the infrared and terahertz spectra with greatly enhanced
responsivity.
The current state-of-the-art infrared detection technology requires either exotic materials or cryogenic conditions to
perform its duty. Implementing infrared detection by coupling infrared tuned antenna with a micro-bolometer offers a
promising technological platform for mass production of un-cooled infrared detectors and imaging arrays. The design,
fabrication, and characterization of a planar slotted antenna have been demonstrated on a thin silicon dioxide (SiO2)
membrane for infrared detection. The planar slotted antenna was chosen due to its ease of fabrication and greater
fabrication tolerance, higher gain and greater bandwidth coveted for the infrared applications. The employment of the
SiO2 membrane technology mitigates the losses due to surface waves generated as the radiation coupling into the
substrates. In addition, by retaining the membrane thickness to be less than a wavelength, the amount of interference is
greatly reduced. A strategically designed planar slotted dipole antenna is implemented along with an integrated direct
current (DC) block enabled by co-fabricated on-chip capacitors between the two DC patches to separate DC and high
frequency signals without the need for sub-micron DC separation line. As a result of this revision, standard UV
photolithography instead of e-beam lithography can be used to fabricate the infrared detectors for mass production. This
research is considered as an important step toward our main goal, which is developing ultrafast infrared detector by
coupling a planar slotted antenna with a metal insulator metal (MIM) tunneling diode.
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