No abstract

Phosphate glasses having composition, 40Na 2 O-10BaO-xB 2 O 3-(50-x)P 2 O 5 , where x = 0-20 mol% were prepared using conventional melt quench technique. Density of these glasses was measured using Archimedes principle. Microhardness (MH) was measured by Vicker's indentation technique. Structural studies were carried out using IR spectroscopy and 31 P and 11 B MAS NMR. Density was found to vary between 2⋅ ⋅62 and 2⋅ ⋅77 g/cc. MH was found to increase with the increase in boron content. 31 P MAS NMR spectra showed the presence of middle Q 2 groups and end Q 1 and Q 0 groups with P-O-B linkages. FTIR studies showed the presence of BO 3 and BO 4 structural units along with the depolymerization of phosphate chains in conformity with 31 P MAS NMR. 11 B NMR spectra showed increase in BO 4 structural units with increasing boron content. The increase in MH with B 2 O 3 content is due to the increase of P-O-B linkages and BO 4 structural units as observed from MAS NMR studies resulting in a more rigid borophosphate glass networks.

This paper presents a detailed design and analysis of fringing and metal thickness effects in a Micro Electro Mechanical System (MEMS) parallel plate capacitor. MEMS capacitor is one of the widely deployed components into various applications such are pressure sensor, accelerometers, Voltage Controlled Oscillator's (VCO's) and other tuning circuits. The advantages of MEMS capacitor are miniaturisation, integration with optics, low power consumption and high quality factor for RF circuits. Parallel plate capacitor models found in literature are discussed and the best suitable model for MEMS capacitors is presented. From the equations presented it is found that fringing filed and metal thickness have logarithmic effects on capacitance and depend on width of parallel plates, distance between them and thickness of metal plates. From this analysis a precise model of a MEMS parallel plate capacitor is developed which incorporates the effects of fringing fields and metal thickness. A parallel plate MEMS capacitor has been implemented using Coventor design suite. Finite Element Method (FEM) analysis in Coventorware design suite has been performed to verify the accuracy of the proposed model for suitable range of dimensions for MEMS capacitor Simulations and analysis show that the error between the designed and the simulated values of MEMS capacitor is significantly reduced. Application of the modified model for computing capacitance of a combed device shows that the designed values greatly differ from simulated results noticeably from 1.0339pF to 1.3171pF in case of fringed devices.

The degradation behaviour of phosphate glass with nominal composition, 40Na 2 O-10BaO-xB 2 O 3 -(50-x)P 2 O 5 , where 0 ≤ x ≤ 20 mol%, was studied in water, HCl and NaOH solutions at room temperature to 60°C for different periods extending up to 300 h. These glasses were synthesized by conventional melt-quench technique. Dissolution rates were found to increase with B 2 O 3 content in the glass. The dissolution rates for the glass having 10 mol% B 2 O 3 were found to be 0⋅002 g/cm 2 and 0⋅015 g/cm 2 in distilled water and 5% NaOH solution, respectively, at room temperature after 225 h of total immersion period, whereas it increased considerably to 0⋅32 g/cm 2 in 5% NaOH at 60°C after 225 h. However, glass samples with x = 15 and 20 mol% B 2 O 3 were dissolved in 5% HCl solution after 5 h immersion. The degradation behaviour has been correlated with the structural features present in the glass. The optical microscopy of the corroded surface revealed that the corrosion mechanism were different in acid and alkali media.

This paper presents design and implementation of a wireless pressure sensor system for biomedical application. The system consists of a front-end Micro-ElectroMechanical System (MEMS) sensing capacitor along with an optimised MEMS-based oscillator for signal conditioning circuit. In this design, vertical fringed comb capacitor is employed due to the advantages of smaller area, higher linearity and larger full scale change in capacitance compared to parallel plate counterparts. The MEMS components are designed in Coventorware design suite and their Verilog-A models are extracted and then imported to Cadence for cosimulation with the CMOS section of the system using AMI 0.6-micron CMOS process. In this paper, an optimisation method to significantly reduce the system power consumption while maintaining the system performance sufficient is also proposed. A phase noise optimisation approach is based on the algorithm to limit the oscillator tail current. Results show that for the pressure range of 0-300 mmHg the device capacitance range of 1.31 pF -1.98 pF is achieved which results in a frequency sweep of 2.54 GHz -1.95 GHz. Results also indicate that a 42% reduction of power consumption is achieved when the optimisation algorithm is applied. This characteristic makes the sensor system a better candidate for wireless biomedical applications where power consumption is the major factor.