The HIRIS project funded by the French research agency aims to develop heteroepitaxial diamond on iridium buffer layers grown on SrTiO3 / Si (001) substrates elaborated by MBE [1]. Indeed, this substrate is promising due to its compatibility with silicon based technologies and it allows up-scaling. Four French groups are involved in this project. A first step consisted in the determination of proper conditions to get epitaxial iridium layers on SrTiO3 / Si (001) substrates. The thermal stability of SrTiO3 overlayers with different thicknesses (between 12 and 40 nm) was investigated by SEM and spectroscopic ellipsometry. This study showed that SrTiO3 layers should be thicker than 30 nm to avoid degradation during iridium deposition. The crystalline quality of SrTiO3 layers grown on Si (001) was improved by optimization of MBE conditions. The best parameters for iridium deposition were determined and high quality iridium buffer layers were grown on SrTiO3 / Si (001) substrates with mosaicity of 0.3° (polar) and 0.1° (azimuthal) measured by XRD. The bias enhanced nucleation (BEN) process which consists in applying a voltage between the CH4/H2 plasma and the sample is up to now the most efficient nucleation technique to obtain diamond heteroepitaxy [2]. BEN was previously applied to Ir buffer layers deposited on bulk SrTiO3 (001) substrates [3]. BEN conditions were successfully tuned to obtain a homogeneous nucleation on 5x5 mm2 Ir / SrTiO3 / Si (001) multilayers [4]. Thin diamond films (i. e. templates) were grown by microwave plasma CVD directly after BEN. These templates were characterized using UV Raman and SEM. A cross-section of a template grown on Ir / SrTiO3 / Si (001) was investigated by High Resolution TEM. The size of diamond templates was recently up-scaled to 7x7 mm2. A thickening of templates was performed under dense MPCVD plasma with growth conditions close to homoepitaxy [5]. Diamond heteroepitaxial films grown on Ir / SrTiO3 / Si (001) were then characterized by XRD, Raman and Cathodoluminescence [6]. The work performed during the HIRIS project well demonstrates the potential of Ir / SrTiO3 / Si (001) substrates to achieve the up-scaling of heteroepitaxial diamond wafers. References [1] G. Niu et al., Appl. Phys. Lett. 95 (2009) 062902. [2] M. Schreck et al., MRS Bulletin 39 (2014) 504-510. [3] N. Vaissière et al., Diam. Relat. Mater. 36 (2013) 16-25. [4] K. H. Lee et al. (to be submitted) [5] J. Achard et al, J. Phys. D, 40 (2007) 6175-6188 [6] H. Bensalah et al. (to be submitted)