Prasenjit Ray

Al-doped ZnO thin-film transistor embedded micro-cantilever as a piezoresistive sensor

In this work, an aluminium-doped zinc oxide (AZO) thin film transistor, embedded in a polymer micro-cantilever, is demonstrated for nano-mechanical sensing applications. This device senses the surface stress due to a change in the carrier mobility of the semi-conducting layer. Due to the low Youngs modulus and high strain sensitivity of the AZO layer, this micro-cantilever shows a deflection sensitivity of 116 ppm per nanometer of deflection. Also, mechanical characterization of these devices shows that the resonance frequency is in the range of a few tens of kilohertz which is suitable for sensor applications.

Development of graphene nanoplatelet embedded polymer microcantilever for vapour phase explosive detection applications

In this work, a graphene based strain sensor has been reported for explosive vapour detection applications by exploiting the piezoresistive property of graphene. Instead of silicon based cantilevers, a low cost polymeric micro-cantilever platform has been used to fabricate this strain sensor by embedding the graphene nanoplatelet layer inside the beam. The fabricated devices were characterized for their mechanical and electromechanical behaviour. This device shows a very high gauge factor which is around ∼144. Also the resonant frequency of these cantilevers is high enough such that the measurements are not affected by environmental noise. These devices have been used in this work for reliable detection of explosive vapours such as 2,4,6-Trinitrotoluene down to parts-per-billion concentrations in ambient conditions.

ZnO Nanowire Embedded Strain Sensing Cantilever: A New Ultra-Sensitive Technology Platform

A novel ultra sensitive micro-cantilever-based technology platform was developed in this letter for strain sensing applications. Sensing mechanism is based on electrical conduction through the ZnO nanowires embedded inside a SU-8 polymer cantilever beam. The lower Youngs modulus of the polymer and the higher strain sensitivity of ZnO nanowires are used to improve the performance of these micro-cantilever devices. Deflection sensitivity of this technology is measured to be 128 ppm/nm. Besides the electromechanical characterization, mechanical characterization has also been performed to measure the resonant frequency of these microcantilever devices, which is shown to be in a few tens of kilohertz range, suitable for nanomechanical sensing applications.

Plastic Deformation Study of Vertical Zinc Oxide Nanowires for Polymer Cantilever-Based Sensor Applications

In this letter, the mechanical properties of piezoelectric ZnO nanowire (NW) films have been measured using a nanoindentation technique. We demonstrated a fabrication process to embed this NW film inside a polymeric (SU-8) cantilever. Mechanical properties of this SU-8/ZnO NW film and cantilever have been measured. The ZnO NWs have been grown vertically using a low-temperature chemical synthesis. The observed value of Youngs modulus for ZnO NW is in the range 72-93 GPa. After embedding this NW film inside a polymer matrix, the Youngs modulus value was reduced to the range 5-19 GPa. The mechanical behavior of the NW-embedded cantilever has also been investigated using the nanoindentation technique. These cantilevers have been shown to be suitable for surface stress-sensing applications.

Optimum design of SU-8 based accelerometer with reduced cross axis sensitivity

The work presented here shows a new design for SU8 based piezoresistive accelerometer, where SU8/carbon black is used as piezoresistors. The accelerometer structure is optimized to generate maximum bending stress at the base of the beams. The structure is inherently temperature insensitive. The design of proof mass is such that the sensitivity to cross axis acceleration is kept within a limit of 4%.

A TFT embedded cantilever (CantiFET) platform for sensor applications

This work focusses on the development of a ZnO based piezo-resistive polymer cantilever sensor platform. Two different approaches have been taken, one based on Al-doped ZnO transistor (TFT) embedded in a polymeric micro-cantilever and another with a ZnO nanowire embedded microcantilever. Low Youngs modulus of SU-8, low process temperature and high strain sensing capability of ZnO makes this platform an attractive option for sensor applications. For both the approaches, electromechanical and mechanical characterization results are reported in this work.

Polymer-Based Micro/Nano Cantilever Electro-Mechanical Sensor Systems for Bio/Chemical Sensing Applications

In this chapter, we present the status of polymer cantilever sensor platforms for biochemical sensing and energy harvesting applications. We introduce a novel process flow for polymer microstructure fabrication called the SPARE MEMS, which involves Spinning of sacrificial/structural layers, Patterning, Anchor formation and the final RElease of the device stack along with the anchor from the substrate. In this process the wafer is spared and is reusable. An organic/thin film FET embedded cantilever devices (CantiFETs) have been demonstrated using this process in order to reduce the noise levels and to achieve high deflection sensitivities. We have also used the SPARE MEMS process to fabricate a variety of other piezoresistive polymer cantilever devices with the highest reported deflection sensitivity (>100 parts-per-million/nm) to surface stress. Electronic circuit design approaches for the detection of ΔR down to sub parts-per-million level of resolution for piezoresistive cantilevers are also discussed. Using various surface coatings, development of sensor systems and sensor nodes for the detection of nitro-based explosive compounds, cardiac proteins, and environmental sensors are demonstrated. For powering the sensors, a novel piezoelectric polymer composite platform has been proposed.

Ultra-sensitive polymeric sensor platforms for environmental sensing applications

In this article, novel technology-platforms are discussed for possible applications in the field of environmental, security and healthcare sensing using polymeric devices. Carbon nanocomposite based microcantilevers and thin-film transistor embedded microcantilevers are discussed for force sensing applications. It is also demonstrated that exposure of ionizing radiation changes the material properties of organic semiconductors which enables the use of organic thin-film transistors (OTFTs) as ionizing radiation dosimeters. An increase in the work-function has been observed by ultraviolet photoelectron spectroscopy for the copper(II) phthalocyanine (CuPc) thin-film upon exposure to ionizing radiation of γ-rays. Furthermore, CuPc based OTFTs are demonstrated as ionizing radiation dosimeters with a silicon nitride encapsulation layer deposited by Hot-wire CVD.

A 8-resistor SU-8 accelerometer with reduced cross axis sensitivity

The MEMS accelerometer has a high cross sensitivity due to proof mass being eccentric. This paper gives results for a SU-8 z-axis accelerometer that uses 8-resistor Wheatstone-bridge to reduce the x-axis and y-axis cross sensitivity by 2 orders of magnitude compared to the conventional 4-resistor Wheatstone-bridge arrangement.