CMOS technology platform for ubiquitous microsensors

Abstract

In this paper we review a range of microsensors based on a common CMOS platform technology. The technology features a CMOS core which includes high temperature tungsten metallization and a post-CMOS deep reactive ion etching step of the substrate to release membranes, where the sensing elements are embedded. In one single process we were able to accommodate a variety of sensors such as gas, humidity, pressure, flow, temperature and infra-red detectors and emitters. The benefits of this platform are: (i) ultra-low power consumption, (ii) small form factor, (iii) high reliability and yield (iv) possibility of on-chip electronics and last but not least (v) low unit price.

A CMOS-Based Thermopile Array Fabricated on a Single SiO2 Membrane

“…The thermopile detector shows enhanced optical absorption in the 8-14 µm waveband (measured using a FTIR spectrometer) with an absorption peak of ~90% at 8.5 µm (see Figure 3a), making it suitable for people presence detection [8]. Optical absorption can be further enhanced by the addition of a high emissivity coating e.g., gold black layer, at the expense of an extra processing step [2]. The uniformity of response to IR illumination per pixel for the 8 × 8 pixel array is shown in Figure 3b.…”

“…Low-cost IR image sensors are increasingly used for a variety of applications, ranging from home appliances and security to automotive and IR cameras for smartphones [1]. These sensors typically consist of an array of thermopiles or bolometers, with the former being inherently insensitive to changes in ambient temperature [1] and being easier to manufacture using low-cost Complementary Metal-Oxide-Semiconductor (CMOS) fabrication processes [2,3], which makes the technology more attractive for commercialization. Thermopile sensors detect a temperature difference ∆T across each thermopile element and are composed of several thermocouples with their hot junctions thermally isolated, typically by a thin dielectric membrane [4,5].…”

“…When the membrane is heated by incident IR radiation, a voltage VT = Nα∆T is generated due to the Seebeck effect [5] which is proportional to the temperature difference across the thermocouple elements ∆T, the Seebeck coefficient α and the number of thermocouples N. The responsivity ℜ is defined as the change in voltage response due to incident optical power (ℜ = dVT/dP) and is highly dependent on the thermal resistance of the device [5]. Micromachining of the silicon substrate can be used to form a membrane with a high thermal resistance to enhance IR heating and thus responsivity [2,3]. A typical array consists of thermopile pixel elements, each fabricated on an isolated membrane, formed by bulk etching of the substrate [1,4].…”

Towards Integrated Mid-Infrared Gas Sensors

“…These requirements can be met in integrated optical systems [17,32], by combining miniaturized optical components [33] and waveguides [34] into highly condensed devices. Integration technologies based on complementary metal-oxide semiconductor (CMOS) processes have clear advantages in size, and power [31,35,36], with the possibility of cost reduction leveraging standard high-volume manufacturing for applications such as integration with consumer electronics [31], or sensor networks for the internet of things (IoT) [15,30].…”

On-Chip Thermal Insulation Using Porous GaN

“…GaN is an increasingly popular material for semiconductor devices, building on its success in optoelectronics and high electron mobility transistors (HEMT) for RF and power applications. More recently, GaN has also been investigated as technology platform for sensing applications [1], due to its enhanced robustness against thermal, mechanical, chemical and radiation damage. For example, many of these efforts are supported by demand for solid-state sensors able to monitor chemical processes, mechanical processing, and outer space exploration.…”