The invention provides a method of making silicon-on-insulator SOI substrates with nitride buried insulator layer by implantation of molecular deuterated ammonia ions ND3+, instead of implanting nitrogen ions as is done in prior art nitride SOI processes. The test jig includes a test circuit substrate with a microstrip line structure, a grounding block and a high frequency signal contact pin. The invention also provides a bodywork element suitable for receiving such a piece, and an assembly constituted by the piece and the element.