Samuel Crand

Conformal Electronics Wrapped Around Daily Life Objects Using an Original Method: Water Transfer Printing

The water transfer printing method is used to transfer patterned films on random three-dimensional objects. This industrially viable technology has been demonstrated to intimately wrap metallic and polymeric films around different materials. This method avoids the use of rigid substrate during the transfer step. Patterns can be transferred to objects without folds even when holed, addressing a challenging issue in the field of conformal electronics. This technique allows high film bending properties to be reached. This promising method enables us to integrate large-area films onto daily life objects. A bent capacitive touchpad is fabricated showing the potential applications of this technology.

pH meter based in Suspended Gate Field Effect Transistors to application in monitoring of water quality

The protocol to monitor the water pH variation during a long time using a full electronic pH-meter consisting of a SGFET (Suspended Gate Field Effect Transistor) is presented after the analysis of the transconductance and the drain current drifts under pH. The main advantages of using this device are its high sensitivity and the ability to integrate it with the electronic treatment into a miniaturized system.

pH sensing from frequency response of SGFET

This paper presents suspended gate field effect transistors (SGFET) used as highly sensitive pH sensors. The devices are there characterized in dynamic mode. The gain, measured versus frequency, is studied for different pH values and shows a resonance frequency depending on the pH value. These results, obtained with different geometries of SGFET, give an opportunity to develop new microsystems, CMOS compatible, highly sensitive to pH.

Direct Electrical Detection of Biological Species

Suspended-Gate FETs, namely SGFET, with sub-micron gap, is shown to be able to detect biological species with very high sensitivity in a large range of concentration. Examples of detection of DNA (through the DelF508 mutation of the cystic fibrosis gene that is widely disseminating in Europe and North America, and one mutation of BRCA1 gene that is the main indication of the possibility for a woman to have breast cancer) and proteins (through the transferrin that is the only carrier of iron in blood) are presented. This very sensitive electrical detection without any labelling is shown to deliver directly readable signal.

Development of suspended gate field effect transistors array-based microsystem for pH measurements

This work presents the specifications of a microsystem which allows pH electrical measurements of solution especially for water monitoring applications. The architecture of this microsystem consists in SGFET (Suspended gate Field Effect Transistor) array-based, control and processing modules. The array is composed of 3 × 3 identical SGFET sensors. Each SGFET can be addressed independently to increase the accuracy and the reliability of the global measurements.

Comparison of NMOS and CMOS TFT inverters fabricated by LPCVD and SPC techniques at low temperature (<600/spl deg/C)

After several experimental studies on improvement of the electrical performances of N-type polysilicon thin-film transistors (NMOS-TFT) fabricated by LPCVD (Low Pressure Chemical Vapor Deposition) and SPC (Solid Phase Crystallization) techniques at low temperature, it was necessary to implement a process to design a complementary TFT cell technology (CMOS-like TFT). This elementary cell is useful indeed essential to design efficient digital circuits. This paper describes the process developed and presents a comparison between two inverters: NMOS-inverter based on the use of two NMOS-TFTs and a CMOS-like TFT inverter. This work has allowed to validate the process and to quantify the improvement of the electrical characteristics such as noise margins, gain and output voltage amplitude.

13.56 MHz rectifier based on a microcrystalline silicon Schottky diodes for RFID application

Nowadays there is a lot of interest for the development of smart and low cost radio frequency identification (RFID) tags to replace barcodes. To achieve this goal of the reduction of production cost the components of RFID tag should be built on flexible substrates. These substrates require the use of materials deposited at low temperature. Our microcrystalline silicon with his deposition temperature (T<165°C) and his structural and electrical performance [1 2] is appropriate to the manufacturing of components dedicated to radio-frequency identification application. In the RFID circuitry one of the main components that should operate at 13.56 MHz is the rectifying device. One way to achieve the high frequency rectification is to fabricate Schottky diode devices [3] We fabricated on corning glass substrate Schottky diodes based on an interface between gold metal and microcrystalline silicon films deposited at low temperature (T<165°C) (Fig.l). The process starts by an isopropanol, acetone and de-ionized water cleaning of the glass substrate to delete any surface impurities. After that three films are deposited, aluminium for cathode contact, Highly N-doped microcrystalline silicon and silicon nitride for to reduce electric field stress at edge terminations and to minimize leakage current of diodes. Then by doing a first photolithographic step silicon nitride is etched to define ohmic bottom contact. Lightly N-doped microcrystalline silicon and gold metal are deposited immediately to form a Shottky contact. Finally a second photolithographic step was done to define the gold contact and to access aluminium bottom contact. Microcrystalline silicon and silicon nitride layers are deposited by using a classical capacitive 13.56 MHz PECVD reactor. Current — voltage measurement were performed at room temperature. Figure 2 shows the I-V characteristics of Au/μc-Si/Al Schottky diodes. For a voltage of −2V and +2V, current is 1.22 μA and 322 μA respectively. The rectifying factor is 264 and he indicates a good rectifying behaviour. The microcrystalline silicon Schottky diodes were then characterized in a rectifier circuit. For an incoming a.c. signal this Schottky diode allowed recovery of rectified voltage at 13.56 MHz. In conclusion Schottky diode based on microcrystalline silicon deposited at T<165 °C was fabricated and will be integrate RFID application on flexible substrates.

Humidity Sensor Thanks Array of Suspended Gate Field Effect Transistor

This work deals with a sensor using array of Suspended Gate Field Effect Transistor (SGFET) to measure the relative humidity (%RH). Technics of microtechnology are used to fabricate a polysilicon bridge with a gap de 0,5 μm which acts as transistor gate. Electrical measures have been realized by sampling mode, involving a sensitivity of -5 μA/%. Also the SGFET humidity sensors are very interesting due to the simplicity to polarize and to analyze the output signal.

An averaging pixel structure using microcrystalline-silicon films prepared at high temperature for AMOLED displays

— A new voltage-addressed pixel using a multiple drive distribution has been developed to improve, in a simple way, the brightness uniformity of active-matrix organic light-emitting-diode (AMOLED) displays. Moreover, circuits were realized using microcrystalline-silicon (μc-Si) films prepared at 600°C using a standard low-pressure CVD system. The developed p-channel TFTs exhibit a field-effect mobility close to 6 cm2/V-sec. The experimental results show that the proposed spatial distribution of driving TFTs improves the uniformity of current levels, in contrast to the conventional two-TFT pixel structure. Backplane performances have been compared using circuits based on μc-Si and furnace-annealed polysilicon materials. Finally, this technology has been used to make an AMOLED demonstration unit using a top-emission OLED structure. Thus, by combining both an μc-Si active-layer and a current-averaging driver, an unsophisticated solution is provided to solve the inter-pixel non-uniformity issue.

A New Active Pixel Design using μc-Si TFT Technology to Improve Brightness Uniformity of Organic Displays

In this paper, we propose and fabricate a new active pixel circuit design integrated on active-matrix organic light-emitting diode (AMOLED) display. Moreover, we have developed a thin film transistor (TFT) based on microcrystalline silicon (μc-Si) active layer for a more efficient process and a better uniformity of driving transistor characteristics. The experimental results show that the emission current uniformity is improved in contrast to the conventional 2-TFT pixel circuit. Thus the proposed averaging driver successfully improves the inter-pixel uniformity.