PILOT LINE FOR CHEMICAL SENSING

Mirphab – Mid-Infrared Photonics Devices Fabrication for Chemical Sensing and Spectroscopic Applications – is an EC funded project granted with € 13 m in a public-private partnership with Photonics21, with the goal of creating a commercially viable pilot line for the fabrication of mid-infrared sensors that is ready for business by 2020. Mirphab has launched its first open call.

There is a growing interest in achieving new chemical sensing devices able to provide enough roughness, in-situ detection and selectivity. These new tools should be easy to integrate in other systems, capable of  analysing the quality and composition of  products from the petrochemical and pharmaceutical industry, suitable for detecting harmful emissions in automotive and environmental monitoring, and able to  provide  non-invasive devices in the medical diagnostics field. One could even dream about sensors integrated in our fridges to scan  for bacteria and warn us when foods are unfit to eat or drink.

Recently, mid-infrared (MIR) spectroscopy has attracted the interest of the sensing industry, due to the possibility of developing low-cost and miniaturized devices able to be integrated in existing equipment for on-line and in-situ monitoring of chemical species. These devices allow real-time and selective detection of the chemical compound of interest. Since MIR light interacts with molecular vibrations, each molecule presents a unique absorption spectrum providing a simple solution for sensing. In this wavelength band, termed the “fingerprint region”, chemicals exhibit intense adsorption features that allow superior detection capabilities and unambiguous identification.

The Mirphab pilot line

The Mid-Infrared Photonics Devices Fabrication for Chemical Sensing and Spectroscopic Applications initiative was launched in January 2016, to serve the European photonic industry by providing high quality MIR photonic components, at reduced investment costs with the aim of encouraging companies to integrate µ-sensors into their products. Mirphab is an open technology platform with a special focus on SMEs, providing services for device design and fabrication from chip processing on wafer level to packaging and testing, as well as training services for pilot line customers.

The Mirphab consortium consists of a core technology group capable of handling both Si and III-V processing that is able to exploit mixed Si/III-V technology to bring new capabilities to sensors that are unavailable today. This core technology group is composed of both established industrial players and major research institutes, covering the whole value chain from epitaxial layer and device design to packaging and module integration. Based on a massive use of IC / MEMS technologies, the pilot aims to enable a variety of new key functionalities for next generation chemical sensing and spectroscopy components at a lower cost, reduced size and lower power consumption.

Assembly of building blocks

The aim of the Mirphab project is to provide each customer with a unique chemical detector / spectrometric system by combining sources, photonic circuits and detectors in a standard packaging, as follows:

  • Spectrometer system: MIR sources, optics, MIR detectors and packaging (Fig. 1).
  • MIR emitters: Interband cascade lasers (ICLs), quantum cascade lasers (QCLs) by Fabry-Perot, distributed feedback Bragg (DFB) or external cavity (EC) technology.
  • Passive components: three integrated photonic platforms are available: a silicon-on-insulator (SOI) waveguide platform, a SiGe/Si platform and a Ge/SiGe platform.
  • MIR detectors: type-II InAs/GaSb superlattice (T2SL), InAsSb and quantum cascade detectors (QCD).
  • Assembly: according to user needs, these components will be chained together either by hybrid or monolithic assembly to realize systems in package (SIP) or systems on chip (SOC) devices.

Sources

The ICL-based sources use 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 grown by molecular beam epitaxy (MBE).

The QCL-based sources 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 a molecular beam epitaxy (MBE) growth of III-V layers (mainly InGaAs/InAlAs).

Detector technology

For cooled operation at 80 K in the 3 – 5 µm regime, the T2SL detector technology is well established as being of very high performance. The challenge here, is to develop uncooled and / or TE-cooled single element operation at extended wavelengths in the 5 – 12 µm range. To achieve this, optically immersed T2SL detectors on GaAs substrates will be developed. Standardization of growth, processing, assembly and characterization procedures will be a priority.

The InAsSb detectors are based on nearly lattice matched to GaSb substrates and are able to detect 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.


Waveguides

In integrated photonics, a waveguide is the equivalent of an optical fibre: light beams can be routed, combined, split or made to interfere anywhere on a planar substrate, using simple optical functions fabricated on the waveguides.

In the last few years, IMEC and CEA-Leti have designed, fabricated, and characterized MIR waveguides for a variety of commercial, scientific and military applications (Fig. 2). Three technologies are available via Mirphab: Si on insulator (SOI) waveguides for applications requiring wavelengths between 2 and 4 µm; SiGe/Si based graded index stack to cover the full (3 – 8 μm) band; and Ge/SiGe technology to address the spectral range above 8 µm. The wavelength at which the molecule of interest absorbs light defines the MIR source, the photonic integrated circuit (PIC) and the detector that will be integrated in your sensing system.

Assembly

The µ-assembly of optical components as well as the packaging of laser and detector chips will be carried out to facilitate integration of the components in the customer’s equipment. To this end, the standardization of tests for industrial manufacturing and long term operation including accelerated aging will be performed. Fabricated QCL and ICL arrays will be used together with the optical silicon combiner to deliver a fully monolithic tunable source.

Packaging and assembly related challenges of MIR laser components for subsequent integration towards µEC modules will also be investigated, including various packaging options, e.g. EPI up chip mounting, flip chip mounting and chip on submount configurations. Related soldering processes and interfaces with respect to soldering materials and temperatures, and contact layer thickness will also be defined.

How to get a chemical sensor customized for your application

Mirphab has launched its first open call. If your company is interested in moving towards the future of real-time chemical sensing, submit your application via the Mirphab website.

The first step is to register your interest by providing basic company information with a short description of the project to be realized. By registering your company, you will be informed as a potential user of new calls for applications. A technological expert is on hand to provide support for completing the application and submitted proposals are evaluated by the Mirphab steering committee.

According to the rules for EC funded projects, successful applicants are granted up to the 70% of the total cost of the project or up to € 230,000, with the remaining 30% covered by the applicant. The grant may be used to cover design, fabrication and assembly costs and the testing of prototypes. In order to bring the developed processes to a wider audience, Mirphab also provides its customers with  in-depth training for platform users and experienced engineers.

The Mirphab pilot line is a unique chance to expand your business in the field of real-time chemical sensors at a minimum capital investment. If you want to  play a significant role in the photonic industrial transformation in Europe, please take note of the following upcoming events: