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| - MEMS/NEMS |
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| - Nanometrology |
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| - Nanofabrication |
| Micro/Nanomechanical Systems |
| Motivation |
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Semiconductor nanomechanical devices enable the pursuit of new physical phenomenon
that can only be observed in these dynamical systems to probe the fundamental nature
of the world as well enabling the development of nanoscience and nanotechnology.
These systems can be manipulated by electrical or optical means permitting applications
such as ultra high sensitivity detectors for weak forces as well as mechanical logic to be developed.
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| Originality |
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Embedding a mechanical oscillator in a GaAs crystal allows the electro-to-mechanical transduction
to be mediated via the piezoelectric effect. This piezoelectric transducer
also enables the parametric excitation of the fundamental mechanical mode.
Uniquely, the parametric resonance has only two stable phases of oscillation
which can be used to encode bit information enabling the development of a mechanical computer.
We also demonstrated the control of the Q-factor and self-excited oscillations in GaAs cantilevers,
which are based on the piezoelectric effect induced by optical carrier excitation.
This technique is applicable to improve sensitivity of the resonators and to develop self-actuators.
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| Impact |
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The opportunity exists to fabricate a new class of devices
whose performance is superior to more conventional systems
for example ultra sensitive force detectors (i.e. mass, spin, charge)
and high speed opto-mechanical switches. Furthermore,
by integrating multiple mechanical oscillators
that are parametrically excited could enable a nanomechanical computer
to be pioneered which could potentially have very low power consumption.
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| Recent Activities |
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Optomechanical photoabsorption spectroscopy of exciton states in GaAs
T. Watanabe, H. Okamoto, K. Onomitsu, H. Gotoh, T. Sogawa and H. Yamaguchi , Appl. Phys. Lett. 101, 082107 (2012) |
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We demonstrate a scheme for the photoabsorption spectroscopy of semiconductors via mechanical vibration characteristics. The thermal vibration of an AlGaAs/GaAs heterostructure-based cantilever sensitively reflects the photoabsorption properties of GaAs because of the optically induced piezoelectric effect. The Q factor and the peak amplitude of mechanical vibration are strongly enhanced near the exciton-related absorption peaks of GaAs at 10K, showing good agreement with reported photoluminescence spectra. |
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An electromechanical membrane resonators
D. Hatanaka, I. Mahboob, H. Okamoto, K. Onomitsu and H. Yamaguchi , Appl. Phys. Lett. 101, 063102 (2012) |
| An electrically active membrane-based mechanical resonator was fabricated from a GaAs/AlGaAs heterostructure. The mechanical motion of the membrane was piezoelectrically excited and detected. The piezoelectric transducer could also excite a range of resonance modes in the membrane that were identified and mapped via optical interferometry. Furthermore, the various mode shapes combined with the piezoelectric transduction could be used to execute mechanical-logic-gates. The development of an electrically active membrane-based mechanical resonator paves the way towards responsive electromechanical detectors and highly functional opto-electro-mechanical systems. |  |
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Phonon-cavity electromechanics
I. Mahboob, K. Nishiguchi, H. Okamoto, and H. Yamaguchi , Nature Physics 8. 387-392 (2012) |
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Photonic cavities have emerged as an indispensable tool to control and manipulate harmonic motion in opto/electromechanical systems. Invariably, in these systems a high-quality-factor photonic mode is parametrically coupled to a high-quality-factor mechanical oscillation mode. This entails the demanding challenges of either combining two physically distinct systems, or else optimizing the same nanostructure for both mechanical and optical properties. In contrast to these approaches, here we show that the cavity can be realized by the second oscillation mode of the same mechanical oscillator. A piezoelectric pump generates strain-induced parametric coupling between the first and the second mode at a rate that can exceed their intrinsic relaxation rate. This leads to a mechanically induced transparency in the second mode which plays the role of the phonon cavity, the emergence of parametric normal-mode splitting and the ability to cool the first mode. Thus, the mechanical oscillator can now be completely manipulated by a phonon cavity. |
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Motion detection of a micromechanical cantilever through magneto-piezovoltage in two-dimensional electron systems
H. Yamaguchi, H. Okamoto, S. Ishihara , and Y. Hirayama , Appl. Phys. Lett. 100, 012106 (2012) |
| We study the strain-induced voltage generation, i.e., piezovoltage, in a two-dimensional electron system under a magnetic field at low temperature. We find its strong magnetic-field dependence, where the voltage increases up to several microvolts at the boundaries between localized and extended electronic states. The order of magnitude of the generated electrical power is comparable to that of the energy dissipation in mechanical vibration, indicating high-efficiency mechanical-to-electrical energy transduction. |  |
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Interconnect-free parallel logic circuits in a single mechanical resonator
I. Mahboob, E. Flurin, K. Nishiguchi, A. Fujiwara,and H. Yamaguchi, Nature Communications 2 (2011) 198 |
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In conventional computers, wiring between transistors is required to enable the execution of Boolean logic functions. This has resulted in processors in which billions of transistors are physically interconnected, which limits integration densities, gives rise to huge power consumption and restricts processing speeds. A method to eliminate wiring amongst transistors by condensing Boolean logic into a single active element is thus highly desirable. Here, we demonstrate a novel logic architecture using only a single electromechanical parametric resonator into which multiple channels of binary information are encoded as mechanical oscillations at different frequencies. The parametric resonator can mix these channels, resulting in new mechanical oscillation states that enable the construction of AND, OR and XOR logic gates as well as multibit logic circuits. Moreover, the mechanical logic gates and circuits can be executed simultaneously, giving rise to the prospect of a parallel logic processor in just a single mechanical resonator. |
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Vibration Amplification, Damping, and Self-Oscillations in Micromechanical Resonators Induced by Optomechanical Coupling through Carrier Excitation
H. Okamoto, D. Ito, K. Onomitsu, H. Sanada, H. Gotoh, T. Sogawa, and H. Yamaguchi, Phys. Rev. Lett. 106 (2011) 036801 |
| Carrier-induced dynamic backaction in micromechanical resonators is demonstrated. Thermal vibration of an n-GaAs=i-GaAs bilayer cantilever is amplified by optical band-gap excitation, and for the excitation power above a critical value, self-oscillations are induced. These phenomena are found in the [110]- oriented cantilever, whereas the damping (deamplification) is observed in the [-110] orientation. This optomechanical coupling does not require any optical cavities but is instead based on the piezoelectric effect that is generated by photoinduced carriers. |  |
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High-sensitivity charge detection using antisymmetric vibration in coupled micromechanical oscillators H. Okamoto, N. Kitajima, K. Onomitsu,1 R. Kometani, S. Warisawa, Sunao Ishihara, and H. Yamaguchi, Appl. Phys. Lett. 98 (2011) 014103 |
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High-sensitivity charge detection using antisymmetric vibration in two coupled GaAs oscillators is demonstrated. The antisymmetric mode under in-phase simultaneous driving of the two oscillators disappears with perfect frequency tuning. The piezoelectric stress induced by a small gate-voltage modulation breaks the balance of the two oscillators, leading to the re-emergence of the antisymmetric mode. Measurement of the amplitude change enables detection of the applied voltage or, equivalently, added charges. In contrast to the frequency-shift detection using a single oscillator, our method allows a large readout up to the strongly driven nonlinear response regime, providing the high room-temperature sensitivity of 147 e/Hz0.5. |
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A symmetry-breaking electromechanical detector I. Mahboob, C. Froitier, and H. Yamaguchi, APPLIED PHYSICS LETTERS 96, 213103 (2010) |
| The dynamical double well potential underpinning the stable oscillation phases in an electromechanical parametric resonator is manipulated via a secondary field excitation applied at the natural frequency of the oscillator. This enables symmetry to be lifted in the dynamical potential well and results in the parametric resonator oscillating with a preferred phase. The ability to break symmetry in the dynamical double well potential permits the realization of a symmetry-breaking detector which can resolve resonance frequency (f0) shifts of δf0/f0 〜 10?7 in a single-shot measurement. |  |
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Optical Tuning of Coupled Micromechanical Resonators H. Okamoto, T. Kamada, K. Onomitsu, I. Mahboob,and H. Yamaguchi, Applied Physics Express 2 (2009) 062202 |
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Frequency tuning of two mechanically coupled microresonators by laser irradiation is demonstrated. The eigenfrequency of a doubly clamped GaAs beam shifts downward in proportion to laser power due to optically induced thermal stress, which modifies the spring constant of the resonator. This frequency tuning enables the control of the coupling efficiency and thus the realization of perfect coupling between the micromechanical resonators, i.e., purely symmetric and anti-symmetric coupled vibration. This optical tuning is a valuable method for the study of physics in coupled resonators as well as for expanding the applications of micromechanical resonators for sensors, filters, and logics. |
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Room temperature piezoelectric displacement detection via a silicon field
effect transistor I. Mahboob, K. Nishiguchi, A. Fujiwara, and H. Yamaguchi, Appl. Phys. Lett. 95, 233102 (2009) |
| An electromechanical oscillator embedded with a two dimensional electron gas is capacitively coupled to a silicon field effect transistor Si-FET. The piezovoltage induced by the mechanical motion modulates the current passing through the Si-FET enabling the electromechanical oscillator’s position to be monitored. When the Si-FET is biased at its optimal point, the motion induced piezovoltage can be amplified resulting in a displacement sensitivity of 6 10?12 mHz?1/2 for a 131 kHz GaAs resonator which is among the highest recorded for an all-electrical room temperature detection scheme. |  |
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Bit storage and bit flip operations in an electromechanical oscillator I. Mahboob and H. Yamaguchi, Nature Nanotechnology 3, 275 (2008) |
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The Parametron was first proposed as a logic-processing system almost 50 years ago. In this approach the two stable phases of an excited harmonic oscillator provide the basis for logic operations. Computer architectures based on LC oscillators were developed for this approach, but high power consumption and difficulties with integration meant that the Parametron was rendered obsolete by the transistor. Here we propose an approach to mechanical logic based on nanoelectromechanical systems that is a variation on the Parametron architecture and, as a first step towards a possible nanomechanical computer, we demonstrate both bit storage and bit flip operations. |
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Controlling quality factor in micromechanical resonators by carrier excitation H. Okamoto, D. Ito, K. Onomitsu, T. Sogawa, and H. Yamaguchi, Applied Physics Express 2, 035001 (2008) |
| The quality factor (Q-factor) of GaAs microcantilevers consisting of Si-doped and undoped GaAs layers can be controlled by tuning the wavelength of the incident laser used for carrier excitation. With laser irradiation to [110]-oriented cantilevers at near-absorption-edge wavelengths, the Q-factor increases with increasing the laser power, whereas shorter-wavelength irradiation decreases the Q-factor. We observed the opposite laser power dependence for [-110]-oriented cantilevers. These results suggest the Q-control is due to the piezoelectric stress generated by the photovoltaic effect. |  |
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Improved resonance characteristics of GaAs beam resonators by epitaxially induced strain Applied Physics Letters 92 (25), 251913 (2008) |
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Micromechanical-beam resonators were fabricated using a strained GaAs film grown on relaxed In0.1Ga0.9As/In0.1Al0.9As buffer layers. The natural frequency of the fundamental mode was increased 2.5-4 times by applying tensile strain, showing good agreement with the model calculation assuming strain of 0.35% along the beam. In addition, the Q factor of 19,000 was obtained for the best sample, which is one order of magnitude higher than that for the unstrained resonator. This technique can be widely applied for improving the performance of resonator-based micro-/nanoelectromechanical devices. |
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Motion detection of a micromechanical resonator embedded in a d.c. SQUID S. Etaki, M. Poot, I. Mahboob, K. Onomitsu, H. Yamaguchi and H. S. J. Van Der Zant, Nature Physics 4, 785 (2008) |
| Superconducting quantum interference devices (SQUIDs) are the most sensitive detectors of magnetic flux and are also used as quantum two-level systems (qubits). Recent proposals have explored a novel class of devices that incorporate micromechanical resonators into SQUIDs to achieve controlled entanglement of the resonator ground state and a qubit as well as permitting cooling and squeezing of the resonator modes and enabling quantum-limited position detection. In spite of these intriguing possibilities, no experimental realization of an on-chip, coupled mechanical-resonator-SQUID system has yet been achieved. Here, we demonstrate sensitive detection of the position of a 2MHz flexural resonator that is embedded into the loop of a d.c. SQUID. We measure the resonator's thermal motion at millikelvin temperatures, achieving an amplifier-limited displacement sensitivity of 10 fm/Hz0.5 and a position resolution that is 36 times the quantum limit. |  |