Olivier Bulteel

High-efficiency solar cell embedded in SOI substrate for ULP autonomous circuits

A low-cost and high-efficiency monocristalline silicon solar cell embedded in a CMOS circuit is proposed for ULP autonomous circuits. Based on a SOI wafer, a photovoltaic lateral diode is realized in the substrate using the fabrication steps of the FD SOI CMOS process of the superposed active circuitry. In case of front side illumination, we achieve 15% efficiency when no CMOS circuit is present, and 11% with an integrated structure in the silicon thin-film overlayer. An efficiency of 19.5% can be further reached in this last case when a 20V bias difference is applied between the thin-film layer and the back contact to deplete the buried oxide / Si substrate interface.

Low-cost miniaturized UV photosensor for direct measurement of DNA concentration within a closed tube container

Highly sensitive measurement of DNA concentration on portable, easy-to-use, low-cost miniaturized equipments without sample waste is challenging. The DNA peak optical absorbance at lambda = 260 nm is a wellknown property already used in the spectrometric measurement of DNA concentration. Existing apparatus are large-sized, expensive and require a manipulation of DNA. In the current work, a low-power, suitable and miniaturized photosensor aiming at a sensitive and direct measurement of DNA concentration has been designed. Direct measurement, i.e. without sample manipulation, implies UV transmission through the translucid tube wall from the closed tube containing the DNA sample in solution. To allow measurements at such low wavelengths, we designed and fabricated photodiodes in SOI technology to ensure a high responsivity in the UV range. Measurements of the photodevice confirmed its responsivity spectrum and magnitudes. These fully integrable photodiodes, fabricated in SOI CMOS technology, can be coupled to a complete signal processing microsystem. Direct measurements at 280 nm optical wavelength of serially diluted DNA within a closed tube (range: 40 pg/ mu L to 400 ng/ mu L in a volume of 45 mu L) generated a monotonic relation between the DNA concentration and the mean of the diode photocurrent induced by light transmission through DNA solution and tube container. Absorbance of the incident UV ray was inversely proportional to DNA concentration. The photosensor compared favorably with other DNA quantitative methods (spectrophotometry, fluorometry, real-time PCR) in terms of sensitivity. Originalities of this work are the use of a thin-film SOI photosensor, the low-cost, portable and adaptable system and the potential of the device for direct measurement of nucleic acid concentration within tube containers without sample manipulation or waste.

Miniaturized and low cost innovative detection systems for medical and environmental applications

Innovative, simple, miniaturized, low-cost and low-power consumption devices are required in future medical applications. In our laboratory we have developed different devices in this field. Firstly, oxide aluminum-coated interdigitated (ID) Al capacitors have been successfully tested for DNA hybridization test (down to 30 pM target concentrations), as well as for specific bacteria recognition (S. Aureus, down to 100 CFU on a sensing area of 200×200 µm2) with an appropriate anti-monoclonal antibody (MoAb) and finally for humidity detection with application in a breath rate monitoring system, an important element for preventive medical studies, which is light, non-invasive, comfortable to wear for the patient. Secondly a complete microsystem enabling the measurement of biomolecules concentration in assay tubes has been developed based on ultraviolet (UV) light absorption with miniaturized LEDs and SOI high-efficiency photodiodes. Our technologies combine high-performance CMOS integrated circuits, sensors and MEMS; operation in harsh conditions (micro power, high-temperature, remote RF link, etc.); very low power consumption; and broad applications in biomedical and environmental sectors. This opens the door to many new emerging applications into medical devices.

Ultra-high-efficiency co-integrated photovoltaic energy scavenger

In this paper, we present a SOI CMOS Ultra-Low-Power (ULP) three-stage charge pump designed to interface photovoltaic (PV) cells co-integrated in the SOI substrate and used as a DC power source. Under an irradiance of 100W/m2, 2 PV cells in series provide a 815mV open-circuit voltage and a 21µA short-circuit current. Indoor measurements have been realized connecting them to one charge pump and the obtained output voltages of both the solar cells and charge pump vs. load are discussed. Improvements and perspectives are provided for an irradiance of 500W/m2. Co-integration is realized on a 2µm multiple-threshold voltage SOI CMOS technology for ULP applications.

Disruptive ultra-low-leakage design techniques for ultra-low-power mixed-signal microsystems

In this paper, we describe applications of a disruptive ultra-low-leakage design technique for drastically reducing the off current in CMOS mixed analog-digital microsystems without compromising the functional performance. The technique is based on a pair of source-connected n- and p-MOS transistors, automatically biasing the stand-by gate-to-source voltage of the nMOSFET at a negative voltage and that of the pMOSFET at a positive level, thereby pushing the off current towards its physical limits. Playing with gate and drain connections, we have created a family of ULP basic blocks: a 2-terminal diode, a 3-terminal transistor and a voltage follower. Using these blocks, we have developed a 7-transistor SRAM cell and an MTCMOS latch with record low stand-by leakage but still high speed performance, highly-efficient power-management units for RF and PV energy harvesting and a microwatt interface for implanted capacitive sensors.

Complete microsystem using SOI photodiode for DNA concentration measurement

In this paper, we describe a complete microsystem allowing the measurement of DNA concentration based on ultraviolet (UV) absorption. The system includes an ultraviolet light-emitting diode (LED) as light source and a silicon-on-insulator (SOI) lateral PIN diode as photodetector. After demonstrating the feasibility of the system with a quartz container, measurements are performed on DNA samples in PCR tubes by direct trans-mittance. The measurement of the sample in the tubes implies no waste neither manipulation of the samples. We study the impact of variation of the different parameters of the system, i.e. the wavelength of the LED, the light power reaching the samples and the bias of the photosensor. We are able to measure responses for DNA concentrations in the range from 400 ng/μL to 4 pg/μL and correlate bacteria concentrations to the induced photocurrent of the diode from 6.1011 spores/mL to 6.107 spores/mL. The system features a present precision of current measurements of 2%. In the optimal case, a limit of detection (LOD) of 0.02 ng/μL has been estimated.

Low-Wavelengths SOI CMOS Photosensors for Biomedial Applications

Biological agents may be characterized (in terms of quantity (or concentration), purity, nature) using optical ways like spectrometry, fluorometry and real-time PCR for example. Most of these techniques are based on absorbance or fluorescence. Indeed, many biological molecules can absorb the light when excited at wavelengths close to blue and ultraviolet (UV). For example, DNA, RNA and proteins feature an absorption peak in the deep UV, more precisely around 260 and 280 nm (Karczemska & Sokolowska, 2001). This work is widely focused on those wavelengths. A biological sample concentration measurement method can be based on UV light absorbance or transmittance, as already known and realized with high-cost and large-size biomedical apparatus. But, often, the difficulties come from the limitation for measuring very small concentrations (close to a few ng/μL or lower) since themeasurement of such small light intensity variations at those low wavelengths requires a precise light source, and very efficient photodetectors. Reducing the dimensions of such a characterization system further requires a small light source, a miniaturized photosensor and a processing system with high precision to reduce the measurement variations. Some light-emitting diodes (LED) performing at those UV wavelengths have recently appeared and may be used to implement the light source. Concerning the optical sensor, while accurate but high-cost photosensors in technologies such as AlGaN and SiC provide high sensitivities in UV lowwavelengths thanks to their semiconductor bandgap (Yotter & Wilson, 2003), the silicon-on-insulator (SOI) layers absorb the photons in that specific range thanks to an appropriate thickness of the silicon. Adding excellent performances of low power consumption, good temperature behavior and high speed (Flandre et al., 1999; 2001), the SOI technology allows the designers for integrating a specific signal processing integrated CMOS circuit to transform the photocurrent into a digital signal for example. This opens the possibility to build a low-cost, complete and portable microsystem, including the light source, the photodetector and a recipient for the sample to characterize. For this chapter, we start with a state-of-the-art describing the current DNA quantification methods with their advantages and disadvantages. Since we will work at low optical wavelengths, we review different ultraviolet light sources that are used in laboratories or in biomedical fields. A description of different photodetectors in various technologies, more especially in SOI, suitable for DNA quantification will then be presented. Afterwards, we 14

Electrical characterization of SOI solar cells in a wide temperature range

In this work the influence of temperature on the characteristics of solar cells implemented in SOI substrate have been presented. It has been shown that the short-circuit current, open-circuit voltage and maximum power increase with temperature reduction. In addition, the fill factor improves at low temperatures, indicating that these solar cells may be succesfully used for space applications or other circuits designed to operate at cryogenic environments.

Ultra-low-power analog and digital circuits and microsystems using disruptive ultra-low-leakage design techniques

In this paper, we describe circuits and microsystems applications of a disruptive ultra-low-leakage design technique for drastically reducing the off current in CMOS analog and digital functions without reducing the functional performance. The technique uses a pair of source-connected n- and p-MOSFETs, implementing an auto-bias of the stand-by gate-to-source voltage of the nMOS transistor at a negative voltage and that of the p-device at a positive level, thereby reducing the off current towards its physical limits. Changing the gate and drain connections, we propose a series of ultra-low-power basic blocks : a 2-terminal diode, a 3-terminal transistor and a voltage follower. These blocks can be combined to yield a 7-transistor SRAM cell and an MTCMOS latch with record low stand-by leakage but still high-speed performance, as well as high-efficiency power-management units for RF and PV energy harvesting and a microwatt interface for implanted capacitive sensors.