The performance of organic field-effect transistors, OFETs, restricts their potential use to applications where low efficiency and short lifetimes are acceptable, although recently the field has evolved rapidly. [1,2] Proposed applications are radiofrequency information tags, e.g., price tags and inventory labels, sensors, and simple displays.[3±6] A simple, low-cost manufacturing process is desired, however such processes usually result in significantly lower device performance. The manufacture of state-of-the-art OFETs today [7] normally requires the device to be processed in an inert atmosphere and to be shielded from oxygen and humidity in the air.[8] The best organic transistors have almost reached the performance levels of amorphous silicon devices and the technology is entering the commercial stage.[9±13]We report on the manufacture and characteristics of a highperformance OFET. The special feature of the device is its ability to take advantage of ambient moisture by using a hygroscopic gate dielectric. (The device is hereafter referred to as hygroscopic insulator field-effect transistor, HIFET.) The all-polymer HIFET can be produced by a solution process using printing techniques onto flexible plastic substrates where all processing steps can be performed without requiring controlled atmosphere. We record a one-hundred-fold enhancement in measured currents at low drive voltages of only a few volts, with good current saturation and current modulation in ambient atmosphere. The static performance of the device characterized by current level and modulation at low voltages (less than 1 V) is greatly enhanced by moisture in the hygroscopic insulator. This study concentrates on the novel device characteristics and proposes an explanation for the device operation mechanism.The HIFET measured in room atmosphere shows excellent performance in terms of current level and modulation, as can be seen from the output curve in Figure 1A. The current saturates at less than 1 V on the drain electrode for a low constant gate voltage (V G varied within less than ±1 V), indicating a threshold voltage close to 0 V. The corresponding transfer curve in the saturated region is shown in Figure 1B, from which the turn on voltage (V to ) and the ON/OFF ratio can be estimated to be 0.4 V and~200, respectively. Here, V to is giv-

The outflow conductance (C(out)) of the cerebrospinal fluid (CSF) system is a parameter considered to be predictive in selection for hydrocephalus surgery. C(out) can be determined through an infusion test. A new apparatus for performing infusion tests in a standardized and automated way was developed. The objective was to evaluate repetitiveness as well as to propose and evaluate a method for real time estimation of the reliability of individual C(out) investigations. Repeated investigations were performed on an experimental model simulating the CSF system, and on 14 patients with hydrocephalus. DeltaC(out), calculated as the 95% confidence interval of C(out), was introduced as an estimate of the reliability of individual C(out) investigations. On the model, no significant difference was found between DeltaC(out) and the actual C(out) variation in repeated investigations (p = 0.135). The correlation between the first and the second patient investigation was high (R = 0.99, p < 0.05), although there was a significant difference between the investigations (p < 0.05). The standard deviation of difference was 2.60 microl (s kPa)(-1). The repetitiveness of C(out) with the new apparatus was high, and DeltaC(out) reflected the reliability of each investigation. This feature has to be taken into account in every individual case, before making a decision or performing research based on measurements of C(out) in the future.

Intraocular pressure (IOP) measurement is performed routinely at every eye clinic. High IOP, which can be a sign of glaucoma, can lead to degeneration of the retina and can cause blindness. In this study we developed a resonator sensor for IOP measurement based on an oscillator consisting of a piezoelectric element made of lead zirconate titanate, a flat contact piece of nylon and a feedback circuit. The aim of this study was to evaluate the new sensor's ability to determine lOP in an in vitro pig-eye model. Six eyes from four pigs were removed and fixed in agar. They were then pressurized by a saline column (10-35 cm H2O) through a cannula inserted into the vitreous chamber. The IOP was measured with the resonator sensor applied to cornea. An Alcon applanation pneumatonometer and a standard Viggo-Spectramed pressure sensor connected to the saline column were used as references. The IOP as measured with the resonator sensor correlated well with the pressure elicited by the saline column for individual eyes (r = 0.96-0.99, n = 60) and for all eyes (r = 0.92, n = 360). The correlation between the resonance sensor and the pneumatonometer was r = 0.92 (n = 360). The pneumatonometer also showed a good correlation with the saline column (r = 0.98, n = 360). We conclude that our in vitro pig-eye model made it possible to induce reproducible variation in IOP, and measurement of that pressure with the newly developed resonator sensor gave very promising results for development of a clinically applicable IOP tonometer with unique properties.

The operating principle of a hygroscopic insulator field-effect transistor has been investigated. The semiconductor poly(3-hexylthiophene) shows an increased conductivity after applying the poly(vinylphenol) (PVP) insulator, which is attributed to an interfacial dipole layer caused by the permanent dipole moment in PVP. The effects of solvents on the transistor device indicate that low molecular weight protic solvents such as water, methanol, and ethanol affect the I-V characteristics significantly, in contrast to 1-propanol and aprotic solvents such as acetonitrile. The presence of a protic solvent inside the device insulator gives rise to an ion-assisted modulation of the transistor source-drain current.