Patent EP-2487793-A1 (EP)
Inventor: GORISSE MARIE
IPC: H01L21/033
Filed: 2012-02-02
Abstract: The method comprises defining geometric parameters of cone-shaped closed inclusions such as holes, of a two-dimension phononic crystal structure, including walls in contact with a heterogeneous matrix by a first angle such as an angle of wall, producing a first series of inclusions having the first angle of wall in the matrix constituted by second medium, providing an upper silicon layer (20) having a surface of a silicon oxide layer on a silicon-on-insulator substrate (10), depositing a resin layer on a surface of the substrate, and defining patterns etched in the resin layer. The method comprises defining geometric parameters of cone-shaped closed inclusions such as holes, of a two-dimension phononic crystal structure, including walls in contact with a heterogeneous matrix by a first angle such as an angle of wall, producing a first series of inclusions having the first angle of wall in the matrix constituted by second medium, providing an upper silicon layer (20) having a surface of a silicon oxide layer on a silicon-on-insulator substrate (10), depositing a resin layer on a surface of the substrate, defining patterns etched in the resin layer, creeping the resin layer to orient the etching patterns, performing an etching operation on the upper silicon layer through the patterns oriented in the resin layer so as to define tapered holes having the angle of wall, removing the resin layer including the etching patterns, and producing a Bragg mirror structure supporting a two-dimensional phononic crystal structure. The inclusions are formed in a first medium that is distributed in the matrix constituted by the second medium for blocking a propagation of acoustic waves in a frequency band such as a stopband. The parameters comprise first geometric angle wall. The defining step comprises: determining a function related to changes in a frequency position of a frequency band such as a stopband with the angle of wall and/or determining a function related to changes in width of the band with the angle of wall; and determining the first angle for the frequency position and/or the width of the band from the determined function. The step of determining the function is carried out by a three-dimensional simulation operation that is performed by finished elements and/or by experience measurements. The step of producing the first series of inclusions comprises depositing a material layer made of aluminum nitride on the substrate, producing a resin mask on the material layer, performing reactive ion etching operation in the material layer to define tapered holes having the angle of wall, and removing the resin mask. An upper silicon layer having a surface of a silicon oxide layer is provided on the substrate. The inclusions have circular, square, hexagonal or triangular geometries, are disposed according to periodic arrangements obtained by receiving a hexagonal elementary mesh or a square or triangular honeycomb, broaden a maximum stopband, are formed by superposed and/or juxtaposed materials, and are filled with the material. The matrix includes a stack of layers.