Inside Paragraf’s Large-Scale Graphene Sensor Foundry

Scientists and engineers have long touted graphene for use in electronic devices due to its excellent electrical conductivity, optical transparency, mechanical strength, and its ability to conduct heat and to remain stable under high temperatures. Graphene’s use in electronics at the commercial level, however, is still limited. That’s in part because it’s much harder to create and integrate single-layer graphene that is required for most (but not all) electronics at large scales. It’s also due to the robust regulatory and certification requirements that graphene, as a new material, has to go through for many high technology applications before it can be used.That said, many advanced technology markets, including sensors, are starting to more widely use the material.

A number of companies around the world have developed graphene sensors, but many have of these have revolved purely around biosensing, with many companies trying to develop advanced COVID test during the pandemic.But Paragraf, a company based in Cambridgeshire in the United Kingdom,has set its sights higher than being a small-scale batch-to-batch producer of graphene sensors. Instead, the company is aiming to become the first graphene foundry that supplies end-users with “blank canvas” graphene field effect transistor (gFET) sensing components that can be tailored to individual needs by users across different industries.

Paragraf believes this approach will make it easier for the company to scale up its manufacturing capabilities. The approach removes regulatory constraints and allows the engineers to just focus on the core technology, rather than having to consider the multitude of scenarios where their sensors could be used and for which they would need to be specifically customized.

Building Blank Canvas gFETs

Paragraf’s sensor elements are a blank canvas, so to speak. The company is building the main sensing surface—the canvas—by growing graphene on a sapphire substrate and adding two contacts with a gate electrode on top. It’s then up to Paragraf’s customers to finalize the sensor based on what they need it to do: “We’re not selling a finished sensor,” says Mark Davis, Paragraf’s director of biosensors, who adds that many different kinds of receptors can be added to the sensor by the user.

By giving the user control over the sensing receptors, it will make it easier for the gFETs to meet regulatory and certification requirements in their respective industries. Paragraf is targeting plenty of applications and industries, including potassium ion sensing in healthcare diagnostics, detecting heavy metals in agricultural wastewater runoff, gas sensing applications in the healthcare, agricultural, and hydrogen energy industries, pH sensing in cell and gene therapy, food and beverage monitoring, and chemical processing applications.

There is also a lot of potential for the gFETs to possess multiplexing capabilities for healthcare diagnostics, where many different biomarkers or chemical components of interest can be measured on the same chip. “Many gFETs only contain 3 to 5 channels, but the size of Paragraf’s FETs means that we can fit up to 100 channels onto a chip,” says Davis, which allows the resulting chip to detect and differentiate more things in a given sample.

Users of Paragraf’s gFETs, according to the company, are starting to develop healthcare diagnostic platforms using these blank canvas sensors for single ion and pH sensing applications because of the gFET’s high sensitivity. “For most healthcare applications, we’re looking at single-use disposable sensors that will cost $1 per sensor,” says Davis. “In the future, so long as we can make over 1 million [sensors] per annum and keep the wafer size below 3 by 3 millimeters, we will be able to get the costs down to this level―expanding the potential and capabilities of graphene sensors, and graphene electronics in general, in real world scenarios.”

Paragraf intends for its graphene field effect transistor to be a blank canvas for users to build upon.Paragraf

Developing gFET Sensor Components at Scale

The gFET being developed by Paragraf is an electrolyte-gated FET. The FET works by placing an electrolyte droplet that the user wants to analyze on the surface of the sensor. The electrolyte’s electrical conductivity creates an electrical bias that changes how the electrons in the sensor’s graphene sheet behave. This also changes the detectable electrical resistance across the graphene sheet—and because graphene’s electrical properties are so good, very small concentrations of ions (including single ions) in the electrolyte sample can be detected.

Paragraf is making the sensors in batches, much like the way the semiconductor industry fabricates wafers full of chips, and are directly depositing the graphene on to the wafers via metal organic chemical vapor deposition and attaching metal contacts on top.

Many chemical vapor deposition techniques grow graphene on copper foil, but the graphene then needs to be transferred to the end device, which can cause structural defects and copper contamination in the graphene that would affect the sensing capabilities of the device. By directly growing the graphene on the wafers, Paragraf is avoiding this to improve the sensing performance of their devices. Davis says that Paragraf is “manufacturing the sensor elements semiconductor-style so that we can miniaturize the sensor elements and fit more sensor elements per chip. The vision for Paragraf is that we are a foundry, and the manufacturer of the sensor components for a final diagnostic solution.”

Davis says that Paragraf can currently fit up to 32 gFETs on a wafer 51 millimeters to a side. The company is in the process of setting up a large-scale manufacturing facility in Huntingdon in Cambridgeshire. Paragraf have also recently acquired another graphene sensor company, Cardea Bio, in San Diego.

Paragraf are also developing graphene Hall effect sensors with a wide dynamic range for both low and high field magnetic measurement applications—from mapping high magnetic fields at CERN and measuring electromagnet fields, to pinpointing current leaks in batteries and measuring the presence of ultra-small magnetic fields inside quantum computers—but these are standard sensor element architecture that don’t require any further input from the end user to be used—they are ready to go. Ultimately, it’s Paragraf’s bet on blank-slate gFETs on which its hopes of creating the first graphene foundry lay.