Method for manufacturing a high-temperature ultrasonic transducer using a lithium niobate crystal brazed with gold and indium

A process for manufacturing a high-temperature ultrasonic transducer, said transducer comprising a steel or metal top electrode, a piezoelectric converter, a steel or metal support ensuring the interface between the converter and the propagation medium of the acoustic waves, a first joint between the support and a piezoelectric material, and a second joint between the converter and the top electrode, comprising the following steps to produce said joints:

• depositing a gold layer then depositing an indium layer on a first face of the converter, and on one face of the steel support;
• the second face of the converter being, independently of the treatment carried out on the face of the electrode, left bare, or covered with a gold layer then an indium layer, or covered with a gold layer or a layer of any other, preferably non-oxidizable, material the electrical and dielectric properties of which are compatible with resistive and/or capacitive, for example, contact electrical coupling of the converter and the electrode;
• the face of the electrode possibly being, independently of the treatment carried out on the second face of the converter, left bare, or covered with a gold layer then an indium layer, or covered with a gold layer or a layer of any other, preferably non-oxidizable, material the electrical and dielectric properties of which are compatible with resistive and/or capacitive, for example, contact electrical coupling of the electrode and the converter;
• stacking the support and the converter, this stack being maintained under pressure, said first face of the converter facing said support;
• producing the indium-and-gold-compound-based first joint via a brazing and diffusing operation,
• said brazing and diffusing operation comprising the following steps:
• a first step of increasing temperature to a first temperature comprised between about 150° C. and about 400° C. and of maintaining this first temperature for a first length of time corresponding to a first plateau;
• and
• a second step of increasing temperature to a second temperature comprised between about 400° C. and about 1000° C. and of maintaining this second temperature for a second length of time corresponding to a second plateau, stacking the top electrode on the converter;
• and
• producing the second joint by bringing the converter and the top electrode into contact.