Micro Structuration of GaAs Surface by Wet Etching: Towards a Specific Surface Behavior

Abstract

Resonant microelectromechanical systems are promising devices for real time and highly sensitive measurements. The sensitivity of such sensors to additional mass loadings which can be increased thanks to the miniaturisation of devices is of prime importance for biological applications. The miniaturisation of structures passes through a photolithographic process and wet chemical etching. So, this paper presents new results on the anisotropic chemical etching of the gallium arsenide (GaAs) crystal used for this application, in several solutions. This paper focuses on the micro/nanostructuration of the sensing surface to increase the sensor sensitivity. Indeed, this active surface will be biofunctionalized to operate in biological liquid media in view of biomolecules detection. Several experimental conditions of etching bath composition, concentration and temperature were examined to obtain a large variety of geometrical surfaces topographies and roughness. According to the orientation dependence of the chemical etching process, the experiments were also performed on various GaAs crystal plates. The bath 1 H3PO4:9 H2O2:1 H2O appeared to be particularly adapted to the fabrication of the GaAs microstructured membrane: indeed, the bath is highly stable, anisotropic, and, as a function of temperature, it allows the production of a large variety of GaAs surface topographies.

GaAs Based on Bulk Acoustic Wave Sensor for Biological Molecules Detection

“…The 625 ±25 m thick GaAs wafer was consequently etched to reach a membrane thickness which is comprised between 50 to 100 m. In order to obtain a flat and undamaged surface, an anisotropic wet etching was done by using orthophosphoric acid based solution. This solution provides smooth surfaces [19], [25] and gives a good control of etch depths at the level of tens angstroms [24]. According to previous studies in our group where several mixtures were tested [19], 1 H 3 PO 4 : 9 H 2 O 2 : 1 H 2 O solution at 0°C seems to give very smooth and flat membranes even for long etching process (etch rate : 0.95 m.min -1 ).…”

“…This solution provides smooth surfaces [19], [25] and gives a good control of etch depths at the level of tens angstroms [24]. According to previous studies in our group where several mixtures were tested [19], 1 H 3 PO 4 : 9 H 2 O 2 : 1 H 2 O solution at 0°C seems to give very smooth and flat membranes even for long etching process (etch rate : 0.95 m.min -1 ). Acid solution was stirred during the process with a magnetic stirrer at 200 rpm to get an uniform etching on the whole wafer.…”

“…Among the different piezoelectric materials, GaAs is the candidate that fulfills most of the requirements, from the integration through the functionalization [16] and including good mechanical piezoelectric properties [17,18].The integration of actuators and micromechanical systems with GaAs-based materials expands the design possibilities for integrated circuits and devices suitable for biosensing applications. In this study, a rapid and low-cost process was investigated [19] to enable large-scale development of piezo-MEMS. The transducer is intended for immunologic biorecognition thanks to the surface functionalization ability of GaAs.…”

Design and microfabrication of a lateral excited gallium arsenide biosensor

“…The etching solutions are composed of an oxidant, an acidic or a basic solution and sometimes a diluent solution. By a variation in composition and concentration of the etching bath, we are able to obtain a large panel of etching rates and patterned surfaces, as already published [26]. The fabrication requirements for the wafer thinning and the membrane microfabrication are not the same.…”

Influence of a Thiolate Chemical Layer on GaAs (100) Biofunctionalization: An Original Approach Coupling Atomic Force Microscopy and Mass Spectrometry Methods

“…This original design, presenting the electronic part separated from the biological interaction reactor, makes it possible to detect a very low mass variation of captured peptides on the surface [3]. This promising sensor structure is obtained using wet etching, which is a low-cost and reproducible process that gives a specific behavior to the surface [4] thanks to adapted microstructuration. Moreover, without the requirement of an added layer [5,6], direct protein grafting is possible through a specific interaction between crystalline facets and specific amino-acid sequences [7,8,9,10,11,12], or genetically engineered proteins [13].…”