Malcolm R. Haskard

A very large integrated pH-ISFET sensor array chip compatible with standard CMOS processes

Abstract The development and preliminary evaluation of a very large pH-sensitive ISFET sensor array chip is reported in this paper. The sensor array chip boasts a 15×16 array of pH-ISFETs with on-chip control and readout circuits. It was designed and fabricated using a novel process which is compatible with standard CMOS technology. This process only required four new mask layers in the design stage and four extra standard processing steps in the fabrication stage. A novel signal processing technique was also employed.

ISFET glucose sensor based on a new principle using the electrolysis of hydrogen peroxide

Abstract An ISFET glucose sensor based on a new principle using the electrolysis of hydrogen peroxide, one of the by-products of the oxidation of glucose, and a Pt electrode actuator is proposed and the characteristics investigated. Compared with the conventional ISFET glucose sensor, the proposed sensor shows an improvement of four times the sensitivity, an extension of the dynamic range to 5 mM glucose concentration, and a faster response of 3 min in 10 mM phosphate buffer solution (pH 7.4, 100 mM NaCl). In addition, the baseline of the sensor response can also be checked, so that the influences of drift of the ISFET and pH change in the sample solution can be eliminated. The sensor shows a large dependence on the buffer concentration. When the buffer concentration is changed from 5 to 20 mM, the sensitivity decreases by a factor of four. However, the high sensitivity, 9 mV mM 1 even in 20 mM buffer concentration, will still allow the sensor to measure glucose concentrations of human blood without the need for dilution.

Anodic bonding technique under low temperature and low voltage using evaporated glass

A silicon-to-silicon anodic bonding process using a glass layer deposited by electron beam evaporation will be described. Wafers are bonded at a temperature as low as 135 °C with an applied voltage as small as 35 Vdc, enabling this technique to be applied to vacuum packaging of microelectronic devices. Experimental results reveal that an evaporated glass layer of more than 1 μm thick is suitable for anodic bonding. Finally, the role of sodium ions in anodic bonding was also studied by investigating the theoretical bonding mechanism and examining the results of secondary ion mass spectroscopy analysis.

A study of two-step silicon anisotropic etching for a polygon-shaped microstructure using KOH solution

Abstract This paper proposes a novel fabrication method for micromechanical structures which are defined by two planes, the (111) plane and a high-index crystal plane. The structure is obtained by a two-step etching process on a (100) silicon wafer using a 40%, 85°C KOH silicon anisotropic etch solution. The (111) plane is created during the first normal anisotropic etching process and the high-index plane is obtained from a second etching step without a silicon dioxide mask. The new plane is considered as a (310) plane, having a 18.43° angle to the (100) plane. A polygon-shaped microstructure can easily be obtained by this method and the structure has excellent reproducibility due to the anisotropic characteristics of the silicon orientation. The method has been sucessfully applied to fabricate a silicon micromould for a plug-type microvalve. The results indicate exact reproduction both in size and shape of the micromould.

Experimental analysis on the anodic bonding with an evaporated glass layer

We performed a silicon-to-silicon anodic bonding process using a glass layer deposited by electron beam evaporation. Corning No 7740 Pyrex glass was used as the source material of electron evaporation. The effects on the bonding process were investigated as a function of the thickness of the glass layer and the concentration of sodium ions in the glass layer. The surface roughness of the glass layer decreased with increasing thickness of the glass layer. It was observed that the deposited glass layers of more than thickness had very small surface roughness. The depth profile of sodium ions showed that the glass layer deposited by electron beam evaporation contained many more sodium ions than the glass layer deposited by sputtering. The silicon-to-silicon bonding process was performed at temperatures in the range of 135 - C with an electrostatic voltage in the range of 35 - . A pull test revealed that the tensile strength of bonded specimens was in the region of 1 - 8 MPa. The role of sodium ions in anodic bonding was studied by investigating the theoretical bonding mechanism and examining the results of secondary-ion mass spectroscopy (SIMS) analysis on the glass layer before and after the bonding process.

Microengineered open tubular columns for GC analysis

Microengineered open tubular (MOT) columns with semi rectangular cross-sections have been designed and fabricated using microengineering techniques. The creation of 100-micrometers wide, 20-micrometers deep, and 125-cm long columns employed isotropic etching on (100) silicon and anodic bonding with a Pyrex 7740 glass cover plate. Column geometry has been optimized to achieve maximum efficiency and allow extreme operating conditions. The walls of the microcolumns were coated with a non-polar liquid stationary phase. Performances of the MOT columns have been demonstrated by their ability to completely separate a series of hydrocarbon mixture in less than 1.25 min under isothermal condition of 150 degrees C. The achievable column efficiencies as measured in terms of theoretical plate height ranged from 0.57 to 1.45 mm, which agreed well with theoretical predictions.

Application of anisotropic conductive films for realization of interconnects in micromechanical structures

A new micromachining process, the application of an anisotropic conductive film (ACF) for micromechanical structures as well as interconnection both mechanically and electrically, is reported. The film acts as a spacer and adhesive as well as an electrical conductor in the vertical direction. The process provides very flexible design scheme and simple fabrication process. New micropump structure was proposed, and simple microstructures have been fabricated and tested successfully. The full details of experiment are reported, experiments where ACF type CP 7621 (Sony Chemical Co) was used to bond p type (100) silicon wafers.

An experiment in Smart sensor design

Abstract The greatest benefits of silicon technology occur when a total system or subsystem is placed on a single chip. Smart sensors, having integrated electronics so that they can match into a standard microprocessor bus system, are an excellent example of the latter. On the one chip all aspects of silicon technology are exploited; a silicon sensor combined with both analog and digital circuitry. While the concept is simple, implementation is still a difficult problem. The Centre set out to construct a low-cost single-chip general-purpose sensor and discovered, amongst other things, that there is a significant increase in silicon area and hence cost penalty when a microprocessor is included on the chip. Consequently the division of responsibility between the smart sensor and the main-system microprocessor becomes an important decision to make. This paper examines the experiences of the Centre in carrying out the experiment so far.

A novel sensing technique based on a sensor array

Abstract A novel sensing approach based on a sensor array has been described. The proposed system employs an array of temperature sensors. The output from each sensor is converted to a one-bit binary signal through a comparator. By analyzing the number of “ones” or “zeros” at the outputs of the comparator, the sensor output is estimated. By further successively reducing the reference voltage range applied to the comparators, the true value of the sensor output can be accurately determined within several iterations. The system has shown a certain degree of redundancy as the measurement does not rely on a particular sensor. Initial experiment using 30 sensors has shown that the relative errors for temperature measurement are between 0.2% and 1.4%. Although the experiment is performed on temperature measurement, the principle of the proposed approach is generic and can be applied to other sensing systems.

A microbioreactor based on interfacial polymerisation and application to flow injection analysis of glucose

A miniature bioreactor is described that uses micromachining fabrication techniques. The bioreactor chamber is created by anisotropic etching of a silicon wafer and attached to a microelectronic sensor by epoxy resin. Any biocatalyst such as an enzyme, a combination of enzymes, or intact viable cells can be contained within the microscopic chamber by an ultra-thin nylon membrane. Tight sealing of the membrane to the silicon wafer surface is achieved by pretreating the anisotropically etched wafer surface with a silylating reagent and then creating the membrane by interfacial polymerisation. By appropriate selection of aqueous and organic phase constituents, the nylon membrane can be covalently linked to the wafer surface by amide bonds. As a simple demonstration for the usefulness of this concept, the microbioreactor has been configured as a glucose sensor in a flow injection cell. Initial results are encouraging and demonstrate that many other applications are feasible.