A CMOS-Based Lab-on-Chip Array for Combined Magnetic Manipulation and Opto-Chemical Sensing

Accepted versio

Design of a single-chip pH sensor using a conventional 0.6-μm CMOS process

A pH sensor fabricated on a single chip by an unmodified, commercial 0.6-/spl μm CMOS process is presented. The sensor comprises a circuit for making differential measurements between an ion-sensitive field-effect transistor (ISFET) and a reference FET (REFET). The ISFET has a floating-gate structure and uses the silicon nitride passivation layer as a pH-sensitive insulator. As fabricated, it has a large threshold voltage that is postulated to be caused by a trapped charge on the floating gate. Ultraviolet radiation and bulk-substrate biasing is used to permanently modify the threshold voltage so that the ISFET can be used in a battery-operated circuit. A novel post-processing method using a single layer of photoresist is used to define the sensing areas and to provide robust encapsulation for the chip. The complete circuit, operating from a single 3-V supply, provides an output voltage proportional to pH and can be powered down when not required

A system-on-chip digital pH meter for use in a wireless diagnostic capsule

This paper describes the design and implementation of a system-on-chip digital pH meter, for use in a wireless capsule application. The system is organized around an 8-bit microcontroller, designed to be functionally identical to the Motorola 6805. The analog subsystem contains a floating-electrode ISFET, which is fully compatible with a commercial CMOS process. On-chip programmable voltage references and multiplexors permit flexibility with the minimum of external connections. The chip is designed in a modular fashion to facilitate verification and component re-use. The single-chip pH meter can be directly connected to a personal computer, and gives a response of 37 bits/pH, within an operating range of 7 pH units

An Extended CMOS ISFET Model Incorporating the Physical Design Geometry and the Effects on Performance and Offset Variation

This paper presents an extended model for the CMOS-based ion-sensitive field-effect transistor, incorporating design parameters associated with the physical geometry of the device. This can, for the first time, provide a good match between calculated and measured characteristics by taking into account the effects of nonidealities such as threshold voltage variation and sensor noise. The model is evaluated through a number of devices with varying design parameters (chemical sensing area and MOSFET dimensions) fabricated in a commercially available 0.35-µm CMOS technology. Threshold voltage, subthreshold slope, chemical sensitivity, drift, and noise were measured and compared with the simulated results. The first- and second-order effects are analyzed in detail, and it is shown that the sensors' performance was in agreement with the proposed model

ISFET Based Microsensors for Environmental Monitoring

The use of microsensors for in-field monitoring of environmental parameters is gaining interest due to their advantages over conventional sensors. Among them microsensors based on semiconductor technology offer additional advantages such as small size, robustness, low output impedance and rapid response. Besides, the technology used allows integration of circuitry and multiple sensors in the same substrate and accordingly they can be implemented in compact probes for particular applications e.g., in situ monitoring and/or on-line measurements. In the field of microsensors for environmental applications, Ion Selective Field Effect Transistors (ISFETs) have a special interest. They are particularly helpful for measuring pH and other ions in small volumes and they can be integrated in compact flow cells for continuous measurements. In this paper the technologies used to fabricate ISFETs and a review of the role of ISFETs in the environmental field are presented

Robust low power CMOS methodologies for ISFETs instrumentation

I have developed a robust design methodology in a 0.18 [Mu]m commercial CMOS process to circumvent the performance issues of the integrated Ions Sensitive Field Effect Transistor (ISFET) for pH detection. In circuit design, I have developed frequency domain signal processing, which transforms pH information into a frequency modulated signal. The frequency modulated signal is subsequently digitized and encoded into a bit-stream of data. The architecture of the instrumentation system consists of a) A novel front-end averaging amplifier to interface an array of ISFETs for converting pH into a voltage signal, b) A high linear voltage controlled oscillator for converting the voltage signal into a frequency modulated signal, and c) Digital gates for digitizing and differentiating the frequency modulated signal into an output bit-stream. The output bit stream is indistinguishable to a 1st order sigma delta modulation, whose noise floor is shaped by +20dB/decade. The fabricated instrumentation system has a dimension of 1565 [Mu] m 1565 [Mu] m. The chip responds linearly to the pH in a chemical solution and produces a digital output, with up to an 8-bit accuracy. Most importantly, the fabricated chips do not need any post-CMOS processing for neutralizing any trapped-charged effect, which can modulate on-chip ISFETs’ threshold voltages into atypical values. As compared to other ISFET-related works in the literature, the instrumentation system proposed in this thesis can cope with the mismatched ISFETs on chip for analogue-to-digital conversions. The design methodology is thus very accurate and robust for chemical sensing

DNA Logic-A novel approach to semiconductor based genetics

In the coming years, genetic test results will be increasingly used as indicators that influence medical decision-making. With chronic disease on the rise and the continuing global spread of infectious disease, novel instruments able to detect relevant mutations in a point-of-care setting are being developed to facilitate this increased demand in personalized health care. However, diagnosis for such demand often requires laboratory facilities and skilled personnel, meaning that diagnostic tests are restricted by time and access. This thesis presents a novel configuration for Ion sensitive Field Effect Transistors (ISFETs) to be used as a threshold detector during nucleic acid base pairs match. ISFET-based inverters are used as reaction threshold detectors to convey the chemical reaction level to a logic output once a threshold has been reached. Using this method, novel DNA logic functions are derived for nucleotides allowing local digital computations. The thesis also presents business models that enable such technology to be utilised in point of care applications, and experiment as results and business models given for an HIV point of care example are proposed

A CMOS-based Lab-on-Chip Array for the Combined Magnetic Stimulation and Opto-Chemical Sensing of Neural Tissue

This paper presents a novel CMOS-based lab-on-chip platform for non-contact magnetic stimulation and recording of neural tissue. The proposed system is the first of its kind to integrate magnetic-stimulation and opto-chemical sensing in a single pixel, tesselated to form an 8 à 8 array. Fabricated in a commercially-available 0.35 ¿m CMOS technology, the system can be intrinsically used for both optical imaging and pH sensing and includes mechanisms for calibrating out sensor variation and mismatch. In addition to sensory acquisition via an integrated 10-bit ADC, a 64-instruction spatiotemporal pattern generator has been embedded within the array for driving the microscale magnetic neural stimulation. In this application the ISFET-based sensors are used to capacitively-couple neuronal charge in close proximity to the floating gate. Optical imaging hardware has also been embedded to provide topographic detail of the neural tissue.Published versio

A Flexible, Highly Integrated, Low Power pH Readout

Medical devices are widely employed in everyday life as wearable and implantable technologies make more and more technological breakthroughs. Implantable biosensors can be implanted into the human body for monitoring of relevant physiological parameters, such as pH value, glucose, lactate, CO2 [carbon dioxide], etc. For these applications the implantable unit needs a whole functional set of blocks such as micro- or nano-sensors, sensor signal processing and data generation units, wireless data transmitters etc., which require a well-designed implantable unit.Microelectronics technology with biosensors has caused more and more interest from both academic and industrial areas. With the advancement of microelectronics and microfabrication, it makes possible to fabricate a complete solution on an integrated chip with miniaturized size and low power consumption.This work presents a monolithic pH measurement system with power conditioning system for supply power derived from harvested energy. The proposed system includes a low-power, high linearity pH readout circuits with wide pH values (0-14) and a power conditioning unit based on low drop-out (LDO) voltage regulator. The readout circuit provides square-wave output with frequency being highly linear corresponding to the input pH values. To overcome the process variations, a simple calibration method is employed in the design which makes the output frequency stay constant over process, supply voltage and temperature variations. The prototype circuit is designed and fabricated in a standard 0.13-μm [micro-meter] CMOS process and shows good linearity to cover the entire pH value range from 0-14 while the voltage regulator provides a stable supply voltage for the system