A Simple Yet Powerful Architecture

G-ray Disruptive Potential is a combination of advanced proprietary technologies for absorber fabrication and monolithic integration:

Absorber fabrication:

  • LEPECVD equipment (Epidavros™) for defect-free SiGe epitaxy on large area silicon wafers
  • MOCVD high-energy absorber layer epitaxy on silicon (or other material) wafers

Monolithic integration:

  • Low-temperature wafer-to-wafer bonding enabling direct conversion
  • Two layers monolithic integration (no bump bonding; no middle TSVs)

Pushing the actual limits of imaging frontiers, our latenium™ detector relies on:

  • Absorber for infrared, low-, medium- and high-energy X-rays
  • Seamless Bonded Interface
  • Electronics

On the absorber side, Silicon Germanium alloy (SiGe) absorbers for low-energy X-ray applications are grown with G-ray’s proprietary epitaxy system, Epidavros™. Absorbers material for medium- and high-energy X-rays include Gallium Arsenide (GaAs) and Cadmium Zinc Telluride (CZT). G-ray will also grow CZT by epitaxy in-house, using a MOCVD system offering unprecedented quality and cost advantages. In addition, G-ray is defining SiGe/MCT absorber specification for infrared.

SiGe-pillar epitaxy by EpidavrosTM system (April, 9th 2018)

Absorber: Epitaxial SiGe pillars as low-energy X-ray absorber grown at G-ray by Epidavros™.

The bonding interface between the specific semiconductor absorber and the CMOS readout is made with the modified EVG®580 ComBond® system. The system was modified by G-ray to obtain a low-energy Argon plasma chamber that enables to clean the wafer surface at the atomic scale, without damaging the crystalline structure, before the bonding process takes place. Additional modifications of the system are explored to optimize both the bonding strength and the electrical charge collection across the bonded interface and reduce costs while improving quality.

Monolithic integration: Low-temperature bonded interface between 2 Si wafers (TEM image: courtesy of Empa).

Intellectual Property

To protect this proprietary disruptive technologies, three Patent Groups have already been filed

Monolithic CMOS integrated pixel detector

Photon Counting CBCT

System and methods to allow charge collection across bonded interfaces

X-Ray Absorber – Si-Ge Epitaxy on Si Wafer

It is a combination of materials that define the sensitivity of the absorption layers.

Seamless Bonded Interface

Low temperature direct wafer-to-wafer bonding process

G-ray with equipment from EV Group can bond (glue together) two silicon wafers with just a very thin amorphous interfacial region.

Direct wafer-to-wafer bonding of sensor wafer and readout wafer is a low temperature direct bonding technology without the need of any special high-temperature metallization layers.

Bump bonding for hybrid pixels remains a dominant cost for detectors. Our Direct Bonding process offers a very significant manufacturing costs reduction and new application opportunities.

Enabling features

  • New sensor materials: higher sensitivity, large area detection
  • Direct conversion: high-speed readout, single photon counting, energy discrimination
  • Two-layer monolithic concept (no bump bonding; no middle TSVs): lower noise, higher bandwith and higher gain due to lower capacitive load;
  • Backside-illumination: 100 percent fill factor; smaller die/pixel size, better resolution, faster speed, better signal-to-noise ratio

Electronics

The readout electronics is developed with partners, following semiconductor industry leading-edge processes, incorporating the most advanced know-how in detector electronic.

  • Pixel Array Detector: direct conversion + single photon counting
  • Smart electronics for signal processing, storage and post-processing.
  • Typical Performance Measures
    • Charge collection efficiency (CCE)
    • Sensitivity (Electron-Hole Pair Creation Energy)
    • Detective Quantum Efficiency (DQE)
    • Modulation transfer function (MTF)
    • Large area deposition ability

Electronics: Novipix ASIC chip demonstrator: 16 x 16 pixels – 100 um pitch.

Manufacturing Equipment

In addition, G-ray has developed its own manufacturing equipment for SiGe epitaxial growth and for low temperature wafer-to-wafer bonding, which is fully operational since Q3-2017.