An Electromechanical Membrane Resonator


Daiki Hatanaka, Imran Mahboob, Hajime Okamoto, Koji Onomitsu, and Hiroshi Yamaguchi
Physical Science Laboratory

   Membrane-based mechanical resonators (MMR) have received much interest because they have high quality-factors [1]. In addition, they also have a large surface area that not only makes them easier to use in optical architectures, but also it makes them more responsive as detectors. However, to date most MMRs have been passive structures with only optical control. The lack of electrical control prevents the development of the MMR for more practical applications. Here, we report a GaAs/AlGaAs-based piezoelectric MMR that enables all electrical transduction of the mechanical motion [2].
   The MMR consists of GaAs (5 nm) / Al0.27Ga0.73As (95 nm) / n-type GaAs (100 nm) heterostructure on an Al0.65Ga0.35As sacrifice layer (3.0 µm). The circular membrane with a diameter of 30 µm was suspended by removing the sacrifice layer through the center hole with hydrofluoric acid as shown in Fig. 1. All measurements in this report were performed in a high vacuum and at room temperature.
   Mechanical oscillations were induced by applying an oscillating voltage to electrode A or B due to the piezoelectric effect and the resulting oscillations were detected by measuring the piezovoltage generated from electrode C. In order to demonstrate its electromechanical functionality, a mechanical logic gate is built with the fundamental (0, 1) mode in the MMR. In the experiment, electrodes A and B are used for binary inputs and electrode C is used for a binary output where electrodes A and C are along the [1(-)1(-)0] orientation and electrode B is along the [1(-)10] orientation as shown in Fig. 1. An excitation of the (0, 1) mode via input A or B results in membrane oscillations with opposite phase due to the opposite sign of the piezoelectric constants in the [1(-)1(-)0] and [1(-)10] orientations in AlGaAs. Therefore, when an actuation of the same magnitude is simultaneously applied to both inputs A and B, mechanical oscillations can be cancelled out, resulting in no piezovoltage at output C. This response from the (0, 1) mode enables the MMR to implement an XOR (AB) logic gate as shown in Fig. 2. Furthermore, we can also demonstrate an OR (AB) logic gate in the first (1, 1) mode using a similar method. Thus, the electrically-active MMR promises functions and performance beyond conventional passive MMRs which could be used to develop a broad range of applications for mechanical resonators.

[1] J. D. Thompson et al., Nature 452 (2008) 72.
[2] D. Hatanaka et al., Appl. Phys. Lett. 101 (2012) 063102.

Fig. 1. The piezoelectric MMR and its measurement set-up.
Fig. 1. An XOR logic gate (AB) in the (0, 1) mode.