Anton Köck, Elise Brunet, Oliver Freudenberg, Christoph Gamauf, Jochen Kraft, Giorgio Mutinati, Thomas Maier, Alexander Nemecek, Franz Schrank, Martin Schrems, Martin Siegele, Jörg Siegert, Stephan Steinhauer, Jordi Teva
We present performance results of SnO2 and CuO nanowire gas sensor devices, where single and multi-nanowire device configurations have been employed in order to optimize sensor design. In particular the response to the target gases CO, H2, and H2S has been measured in dry and humid air; both the SnO2 and CuO nanowire sensors are able to detect CO in the low ppm concentration range, which is important for environmental monitoring. The CuO multi-nanowire devices show an extraordinary high response to H2S with sensitivity in the low ppb concentration. We present our developments of CMOS technology based micro-hotplates, which are employed as platform for gas sensitive thin films and nanowires. Potential heterogeneous integration of nanowires on the micro-hotplate chips as well as an approach towards gas sensor arrays is discussed. We conclude that CMOS integrated multi-nanowire gas sensors are highly promising candidates for the practical realization of multi-parameter sensor devices for indoor and outdoor environmental monitoring.
The 0.35μm HV-CMOS process technology utilizes several junctions with different doping levels and depths. This process supports complete modular 3V and 5V standard CMOS functionality and offers a wide set of HV transistor types capable for operating voltages from 20V to 120V made available with only 2 more mask adders [1]. Compared to other reported integration of photo detection functionalities in normal CMOS processes [2] or special modified process technologies [3] a much wider variety of junction combinations is already intrinsically available in the investigated technology. Such junctions include beside the standard n+ and p+ source/drain dopings also several combinations of shallow and deep tubs for both p-wells and n-wells. The availability of junction from submicron to 7μm depths enables the selection of appropriate spectral sensitivity ranging from ultraviolet to infrared wavelengths. On the other side by appropriate layouts the contributions of photocurrents of shallower or deeper photo carrier generation can be kept to a minimum. We also show that by analytically modelling the space charge regions of the selected junctions the drift and diffusion carrier contributions can be calculated with a very good match indicating also the suppression of diffusion current contribution. We present examples of spectral responsivity of junction combinations optimized for peak sensitivity in the ranges of 380-450nm, 450-600nm or 700-900nm. By appropriate junction choice the ratios of the generated photo currents in their respective peak zones can exhibit more than a factor of 10 compared to the other photo diode combinations. This enables already without further filter implementation a very good spectral resolution for colour sensing applications. Finally the possible junction combinations are also assessed by the achievable dark current for optimized signal to noise characteristic.
We report on a new and very cost effective way to integrate PIN photo detectors into a standard CMOS process. Starting
with lowly p-doped (intrinsic) EPI we need just one additional mask and ion implantation in order to provide doping
concentrations very similar to standard CMOS substrates to areas outside the photoactive regions. Thus full functionality
of the standard CMOS logic can be guaranteed while the photo detectors highly benefit from the low doping
concentrations of the intrinsic EPI. The major advantage of this integration concept is that complete modularity of the
CMOS process remains untouched by the implementation of PIN photodiodes. Functionality of the implanted region as
host of logic components was confirmed by electrical measurements of relevant standard transistor as well as ESD
protection devices. We also succeeded in establishing an EPI deposition process in austriamicrosystems 200mm wafer
fabrication which guarantees the formation of very lowly p-doped intrinsic layers, which major semiconductor vendors
could not provide. With our EPI deposition process we acquire doping levels as low as 1•1012/cm3. In order to maintain
those doping levels during CMOS processing we employed special surface protection techniques. After complete CMOS
processing doping concentrations were about 4•1013/cm3 at the EPI surface while the bulk EPI kept its original low
doping concentrations. Photodiode parameters could further be improved by bottom antireflective coatings and a special
implant to reduce dark currents. For 100×100μm2 photodiodes in 20μm thick intrinsic EPI on highly p-doped substrates
we achieved responsivities of 0.57A/W at λ=675nm, capacitances of 0.066pF and dark currents of 0.8pA at 2V reverse
voltage.
PIN photodiodes are semiconductor devices widely used in a huge range of applications, such as photoconductors,
charge-coupled devices and pulse oximeters for medical applications. The possibility to combine and to integrate the
fabrication of the sensor with its signal conditioning circuitry in a CMOS process allows device miniaturization in
addition to enhance its properties lowering the production and assembly costs. This paper presents the design and
characterization of silicon based PIN photodiodes integrated in a CMOS commercial process. A high-resistivity, low
impurity substrate is chosen as the start material for the PIN photodiode array fabrication in order to fabricate devices
with a minimum dark current. The dark current is studied, analyzed and measured for two different starting materials and
for different geometries. A model previously proposed is reviewed and compared with experimental data.
PIN photodiodes are semiconductor devices widely used in a huge range of applications, such as photoconductors,
charge-coupled devices, and pulse oximeters. The possibility to combine and to integrate the fabrication of the sensor
with its signal conditioning circuitry in a CMOS process flow opens the window to device miniaturization enhancing its
properties and lowering the production and assembly costs. This paper presents the design and characterization of silicon
based PIN photodiodes integrated in a CMOS commercial process. A high-resistivity, low impurity float zone substrate
is chosen as the start material for the PIN photodiode array fabrication in order to fabricate devices with a minimum dark
current. The photodiodes in the array are isolated by a guard ring consisting of a n+-p+ diffusions. However, the
introduction of the guard ring design, necessary for photodiode-to-photodiode isolation, leads to an increase of the
photodiodes dark current. In this article, the new parasitic term on the dark current is identified, formulated, modelled
and experimental proven and has finally been used for an accurate design of the guard ring.
In this work, we present a non-linear electromechanical model of an electrostatically excited cantilever that can be used to perform system level electrical simulations. This model is implemented by using an analog hardware description language (VHDL-AMS) that allows its use in a common IC CAD environment like CADENCE. Small-signal and large-signal simulations are performed and the results are compared with a simple linear model (RLC//C) showing the benefits of this model. This model is validated by its fit with the experimental results obtained from a monolithic sub-micrometer cantilever based sensor
A Micro Electro Mechanical System (MEMS) for mass detection is presented. It has been developed by the monolithic integration of the mechanical transducer with the CMOS control circuit. The sensor transducer consists on an array of four resonating cantilevers; oscillation is achieved by electrostatic excitation. The independent control on each cantilever of the arrays allows multiple sensing on a single device. The microresonators are fabricated on polysilicon in a compatibilized process with the front-end CMOS circuitry. The readout of the cantilevers oscillation is achieved by a current amplifier. Expected Mass resolution in air is 80 ag/Hz.
KEYWORDS: Sensors, Transducers, Field effect transistors, Microelectromechanical systems, Ferroelectric materials, Diodes, Capacitance, Voltage controlled current source, Bridges, Control systems
The aim of this paper is to report the experimental setup designed, developed and tested in order to achieve the first vibrating mode of a lateral cantilever with mechanical excitation. The on-plane oscillating cantilever is the basis of a proposed mass sensor with an expected resolution in the atto-gram scale. In a first system design, the cantilever is driven electrostatically by an electrode, which is placed parallel to the cantilever. The cantilever is driven to its first resonant mode applying an AC voltage between the cantilever and a driver. Also, a DC voltage is applied to increase the system response. The signal read-out of the transducer is the capacitive current of the cantilever-driver system. The mass sensor proposed, based on this cantilever-driver structure (CDS), is integrated with a CMOS circuitry in order to minimize the parasitic capacitances, that in this case take special relevance because of the low level output current coming from the transducer. Moreover, the electrostatic excitation introduces a parasitic current that overlaps the current due to the resonance. The mechanical excitation is an alternative excitation method which aim is to eliminate the excitation current. Here we describe the experimental facilities developed to achieve mechanical excitation and report preliminary results obtained by this excitation technique. The results are complemented with dynamic simulations of an equivalent system model that are in accordance with the experimental values.
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