CMOS‐compatible nanoscale gas‐sensor based on field effect

Abstract

The integration of a solid state gas sensor of the metal oxide sensor type into CMOS technology still is a challenge because of the high temperatures during metal oxide annealing and sensor operation that do not comply with silicon device stability. In the presence of an external electric field sensor sensitivity can be controlled through a change of the Fermi energy level and consequently it is possible to reduce the operation temperature. Based in this effect, a novel field effect gas sensor was developed resembling a reversed insulated gate field effect transistor (IGFET) with the thickness of gas sensing layer in the range of the Debye length (L-D). Under these conditions the controlling electrical field reaches the sensitive surface and a modulation of the Fermi energy level occurs, producing an effective control of gas sensitivity and sensor response. In this paper several aspects are treated, like technological fabrication process, complete sensor characterization by means of an electrical model and sensor response measurements. Other effects as base-line drift effects and layer thickness implications also are studied

Sensitivity-Selectivity Trade-Offs in Surface Ionization Gas Detection

“…Inducing such effects requires surface electrical fields of more than 1×105 V/cm and small air gaps in the order of 1 μm or below, if battery-compatible low-voltage operation is desired. As generating such small air gaps requires methods of multi-wafer micro-assembly, this latter option is not usually followed [18].…”

“…In the RES mode, gas adsorption is monitored via changes in the in-plane resistivity of the MOX sensing layers. The suspended gate electrode is not normally present but may be used to modify gas adsorption processes via the electro-adsorption effect [16,17,18]. In the SI readout mode, changes in gas adsorption are monitored by observing flows of positive ions crossing the thin air gap ( d air ~0.1–1 mm) in between the heated MOX layer and the negatively biased counter electrode.…”

Co‐adsorption processes, kinetics and quantum mechanical modelling of nanofilm semiconductor gas sensors

“…The measurements are realized with a nanothin‐film gas sensor using field effect control as described earlier 8. The sensing layer (SnO 2 ) consists of a polycrystalline thin film of 45 nm which lies in the range of several Debye lengths.…”

B7.3 - Field Effect SnO2 Nano-Thin Film Layer CMOS-Compatible

“…Only then an effective variation of the Fermi level occurs, producing an excellent control over the adsorption and desorption of all weakly and strongly bound gas molecules according to Wolkenstein adsorption statistics [5]. Sensitivity thickness layer d was sufficiently long compared to L D to enable sensing but short enough to influence unbound molecules [9]. Debye length is given by:…”

“…These external electric fields open the possibility of an electrical control of the energy levels (Fermi-level) and therefore gas sensitivity modulation on the metal-oxide surface, see Fig.1. Because of this fact, they are enabled to operate with relative low temperature (150° C -200° C) [1]- [9]. This approach enables the integration into CMOS technology together with the signal processing and information systems and eliminates the need for hybrid system setup.…”