FEATURE PORTABLE SPECTROSCOPY
summer, the results of which will be very encouraging for the photonics industry as a whole, according to Xiong, as they will provide a practical validation of the capabilities of chip-scale optical trace gas sensor technology.
Si-Ware Systems’ NeoSpectra Micro spectrometer can be mass-produced for consumer applications g
the free-space sensor, despite having 75 per cent less light interacting with the air compared to the free-space design. While the new device offers higher
levels of integration than free-space optical sensors, this does result in a reduced interaction path between the trace gas and the light, meaning the parts-per-billion sensitivities of benchtop spectroscopic gas analysers are currently unachievable at this scale. ‘You are limited to the interaction you
can get on a centimetre-scale chip,’ Xiong explained. ‘On the silicon photonic chip, the light in the waveguides is also mostly confined within a silicon waveguide, which… can’t really be made any longer without compromising the signal-to-noise level at the detector, as light experiences propagation losses as it travels along the waveguide. This is a design trade-off we have to make when building integrated sensors – how much interaction you can achieve without experiencing too much loss.’ More applications for the new
spectroscopic gas sensor could be enabled if its sensitivity was increased even further, according to Xiong, which the researchers plan to achieve using longer wavelengths in the mid-infrared range. ‘By using a wavelength of 3µm it would be possible to have a 100-times increase in sensitivity to methane,’ he explained. ‘This is a direction that we are excited about as it will require new sets of materials and a new set of challenges to overcome.’ While the new device can be
manufactured predominately with standard high-volume fabrication methods, the IBM researchers have also developed their own unique process that allows them to
22 Electro Optics March 2018
integrate multiple photonics components onto a single chip. ‘We have invented a new packaging and assembly process that enables us to bring the laser onto the chip, which is one of the big challenges with silicon photonics and sensing, as silicon does not lase,’ Xiong explained. ‘We designed an indium phosphide (InP) gain chip and used a supplier’s standard manufacturing process to procure those as chiplets. We then invented a very special bonding technique
“Our mirrors have to be very vertical and smooth, and we have to be able to etch down at a pretty significant depth to achieve this”
to flip chip assemble these chiplets onto a silicon photonics chip containing the rest of the methane sensor components,’ Xiong continued. ‘Not only are they mechanically bonded, electrically and thermally but they also make sure the light can be coupled very efficiently with low loss from the InP chiplets onto the silicon photonics chip. ‘We’ve designed it so that this technology can be manufactured in a process that self-aligns the two chips together with sub-micron precision, so that a low-loss interface can be achieved without the use of high-precision pick and place tools. This assembly process can also be scaled up for wafer-scale processing,’ Xiong added. IBM’s new silicon photonic methane sensor will be deployed in a number of upcoming oil and gas industry leak detection and quantification field tests this
Making the small even smaller Si-Ware Systems’ (SWS) spectroscopic scaling efforts have resulted in a miniaturised NIR spectral sensor featuring an entire micro interferometer integrated onto a single 1 x 1cm MEMS chip, with the company having reproduced certain benchtop spectrometer components in a unique confined format. ‘We’ve recreated the moving mirror – the motor is now a MEMS actuator, allowing the mirror to move forward and back – the silicon beam splitter and the fixed mirror [of a benchtop FTIR spectrometer],’ said Scott Smyser, executive VP of worldwide marketing and business development at SWS. ‘Getting all of these components on such a small chip is enabled through our SiMost process, which is at its core a standard MEMS process, with some additional IP concerning the design that allows us to instead integrate optics at this scale. ‘With a standard MEMS process – for
example for an inertial sensor – you’re not using optics, so you’re not concerned about verticality or smoothness of the surfaces. For us, however, our mirrors have to be very vertical and smooth, and we have to be able to etch down at a pretty significant depth to achieve this… this is where some of our IP comes in, allowing us to do it with optics.’ These differences do not necessarily
mean that SWS chips cannot be manufactured in a standard MEMS fab, using conventional components and processes, according to Smyser. SWS’s first-generation product using
the micro interferometer MEMS chip is the NeoSpectra Module, an FT-NIR spectrometer about the size of a deck of playing cards that also includes an electronics board containing a specially designed ASIC, a single InGaAs photodetector and optical fibres. The device started shipping in 2016 for approximately $1,000 and the firm has sold thousands of units. It has been integrated into systems such as handheld soil analysis tools and portable analysers for the oil and gas industry. Through recent efforts, SWS has been
able to scale this technology down even further to produce the NeoSpectra Micro, a chip-sized, OEM NIR spectral sensor with a core module size of 18 x 18 x 4mm, priced at around $100. The device was recently highlighted for winning SEMI’s Technology
@electrooptics |
www.electrooptics.com
g
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44
