Evaluating injection and transport properties of organic field-effect transistors by the convergence point in transfer-length method Appl. Phys. Lett.Efficient charge injection from a high work function metal in high mobility n -type polymer field-effect transistors

Extensive research on organic field-effect transistors (OFETs) performed to date investigated separately the electronic contact and the gate dielectric interfaces but rarely probed the relation between the two. In this report, the strong impact of the gate dielectric on the contact resistance (R c ) is revealed. With the same semiconductor dioctylbenzothienobenzothiophene (C8-BTBT) and the same device configuration, the R c value varies greatly from 10 to 66 kΩ•cm depending on the gate dielectric interfaces. Also, the gatevoltage dependency of R c exhibits an unexpectedly large discrepancy when different dielectrics are used. Intuitive comprehension points to the possibility that the gate dielectric interface affects the morphology of semiconductor and thus the charge injection. However, from microstructure study, albeit the semiconductor film exhibits structural defects on certain dielectrics, the impact on the injection is not crucial. Instead, bias-stress test correlates well with the contact resistance on different dielectric interfaces. At a quantitative level, gate-voltage-dependent R c can be described by taking into account the different charge trapping induced by the gate dielectrics. The origin of the varied R c is thus attributed to the trapped charges, which screen the gate field and reduce the carrier mobility simultaneously. A general method is proposed to examine whether the charge injection is significantly influenced by the charge trapping effect due to the gate dielectrics.

More than one third of about 38 million adults 65 and older fall each year in the United States. To address the above problem we propose to develop an acoustic fall detection system (FADE) that will automatically signal a fall to the monitoring caregiver. As opposed to many existent fall detection systems that require the monitored person to wear devices such as accelerometers or gyroscopes at all times, our system is completely unobtrusive by not requiring any wearable devices. To reduce the false alarm rate we employ an array of acoustic sensors to obtain sound source height information. The sound is considered a false alarm if it comes from a source located at a height higher than 2 feet. We tested our system in a pilot study that consisted of a set of 23 falls performed by a stunt actor during six sessions of about 15 minutes each (1.3 hours in total). The actor was previously trained by our nursing collaborators to fall like an elderly person. The use of height information reduced the false alarm hourly rate from 32 to 5 at a 100% fall detection rate.

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