Based on a massive use of IC/MEMS technologies, the pilot line will enable a variety of new key functionalities for next generation of chemical sensing and spectroscopy, allowing low-cost, power consumption and size reduction. Where required, the development of novel process modules will exploite the capability of a mixed Si/III-V technology bringing new capabilities to sensors, opening the way to a number of applications not addressed with the technologies and components available today.
The spectrometer system offered by MIRPHAB will consist of: MIR Sources, Optics, MIR Detectors and Packaging. Interband Cascade Lasers (ICLs), Quantum Cascade Lasers (QCLs) are the MIR emitters available working by Fabry-Perot, Distributed Feedback Bragg (DFB) or External Cavity (EC) technology. Regarding passive components, three integrated photonic platforms will be available: a silicon-on-insulator (SOI) waveguide platform, a SiGe/Si platform and a Ge/SiGe platform. MIR detectors available are type-II InAs/GaSb superlattice (T2SL), InAsSb and Quantum Cascade Detectors (QCD). Finally, according to the specifications provided accompanied by the users, these components will be chained together either by hybrid or monolithic assembly to realize Systems In Package (SIP) or Systems On Chip (SOC) devices.
ICL uses injected electrons to emit multiple photons by interband transitions and to produce coherent radiation in the wavelength range 3-6 µm. ICL are fabricated by stacking layers of InAs, GaSb, AlSb and related alloys growth by Molecular Beam Epitaxy (MBE). The multilayer structure is then manufactured into laser waveguides with incorporated structurer for wavelength selection and/or broadband emission. MIRPHAB is working on:
- mode matched Distributed Feedback Bragg (DFB) devices for integration with waveguide structures,
- gain chips for the implementation in µ-EC modules for wide tunability,
- monolithic ICL DFB arrays for integration with multiplexer structures.
QCL are unipolar devices in which the laser emission is achieved through the use of intersubband transitions in a repeated stack of semiconductor multiple quantum well layers achieving coherent radiation in the wavelength range 4-12 µm. QCL stacks are fabricated by Molecular Beam Epitaxy (MBE) growth of III-V layers (mainly InGaAs/InAlAs). The multilayer structure is then manufactured into laser waveguides with incorporated structurer for wavelength selection and/or broadband emission. MIRPHAB is working on:
- industrialization of External Cavity (EC-QCL) aggregating functions to provide a tunable source with up to 4% fully electrical tuning,
- extended tunablility single frequency metal grating lasers DFB-QCL,
- QCL arrays for monolithic broadly tunable (MG-QC-Arrays),
- optimization of the fabrication process from EPI growth of active structures to the manufacturing process to obtain sustainable production costs.
Type-II Superlattice (T2SL) Detectors
For cooled operation at 80K in the 3-5 µm regime the T2SL detector technology is well established and has very high performance. The challenge here is to develop uncooled and/or TE-cooled single element operation at extended wavelengths in 5-12 µm range. For that, optically immersed T2SL detectors on GaAs substrates will be developed. Standardization of growth, processing, assembly and characterization procedures will be a priority.
Detector are based on InAsSb nearly lattice matched on GaSb substrate for detection at a wavelength below 4.6 µm. The sensor is based on a double barrier hetero-structure optimized for operation between 250 K and room temperature.
Quantum Cascade Detectors (QCD)
QCD for peak wavelengths of 5.6 µm, 8 µm and 14 µm are available. Using simulation tools, peak wavelengths will be tuned in the range from 5.5 µm to larger 12 µm with new designs and predicted performances when re
quired by other partners. A new design allowing the co-integration of QCD/QCL will be developed. A set of specifications will be provided for every wavelength: detectivity, cutoff wavelength and operating temperature.
Mir passive components and integrated photonics
In Integrated Photonics a waveguide and its cladding is the equivalent of an optical fiber: Light beams can be routed, combined, split or make interfering anywhere on a planar substrate using simple optical functions fabricated on the waveguides. In the last few years imec & CEA-LETI have designed, fabricated, and characterized MIR waveguides with for a variety of commercial, scientific and military applications. Three technologies are available via MIRPHAB: Si on Insulator (SOI) waveguides for applications requiring wavelengths up to between and 4 µm, SiGe/Si based graded index stack to cover the full [3-8μm] band and Ge/SiGe technology in order to address spectral range above 8 µm.
Packaging and assembly
The µ-assembly of optical components as well as the packaging of laser and detector chips will be carried out in order to facilitate the integration in the customer equipment. On the other hand the standardization of tests for industrial manufacturing and long term operation including accelerated aging will be performed.
With respect to µ-assembly, fabricated QCL and ICL arrays will be used together with the optical silicon combiner in order to deliver a fully monolithic tunable source. Packaging and assembly related challenges of MIR laser components for subsequent integration towards µEC modules will be investigated. In this context also various packaging options (EPI up chip mounting, flip chip mounting, chip on submount configurations etc.) with the corresponding requirements are investigated and the related soldering processes and interfaces with respect to soldering materials and temperatures, contact layer thickness… will need to be defined.