Validity of the parabolic effective mass approximation in silicon and germanium n-MOSFETs with different crystal orientations

This paper investigates the validity of the parabolic effective mass approximation (EMA), which is almost universally used to describe the size and bias-induced quantization in n-MOSFETs. In particular, we compare the EMA results with a full-band quantization approach based on the linear combination of bulk bands (LCBB) and study the most relevant quantities for the modeling of the mobility and of the on-current of the devices, namely, the minima of the 2-D subbands, the transport masses, and the electron density of states. Our study deals with both silicon and germanium n-MOSFETs with different crystal orientations and shows that, in most cases, the validity of the EMA is quite satisfactory. The LCBB approach is then used to calculate the values of the effective masses that help improve the EMA accuracy. There are crystal orientations, however, where the 2-D energy dispersion obtained by the LCBB method exhibits features that are difficult to reproduce with the EMA model

Design trade-offs in amorphous indium gallium zinc oxide thin film transistor based bio-signal sensing front-ends

With the advent of the Internet of things, wearable sensing devices are gaining importance in our daily lives for applications like vital signal monitoring during sport and health diagnostics. Amorphous indium gallium zinc oxide (a-IGZO) thin film transistors (TFTs) fabricated on flexible large-area substrates are a very interesting platform to build wearable sensing devices due to their flexibility, conformability to the human body, and low cost. For this paper four different bio-signal sensing front-end circuits based on a-IGZO TFTs are designed, fabricated, measured and compared, focusing on three performance indicators which are in a trade-off: power efficiency factor (PEF), area occupation and input impedance. Considering a 200 Hz bandwidth, the measured PEF varies between 4.7 × 105 and 7.5 × 106. The area occupation spans from 4.2 to 37 mm2, while the input impedance at 1 Hz varies from 5.3 to 55.3 MΩ. The front-ends based on diode-load amplifiers are compact but have the lowest input impedance and need external capacitors; a front-end exploiting positive feedback impedance boosting has the highest input impedance and is fully integrated on foil, but occupies the largest area

A conformable active matrix LED display

Conformable and stretchable displays can be integrated on complex surfaces. Such a display can assume the shape of a conformed surface by simultaneous multi-dimensional stretching and bending. Such technology provides new opportunities in the field of display applications, for example wearable displays integrated or embedded in a textile or onto complex surfaces in automotive interiors. In this work we present a conformable active matrix display using LEDs mounted on an amorphous Indium-Gallium-Zinc Oxide (a-IGZO) TFT backplane. A two-transistor and one capacitor (2T-1C) pixel engine based backplane, fabricated on polyimide substrate, is used to drive LEDs. Rigid LED pixels are connected via meandered copper film. The meander interconnections have been optimized with respect to their electrical and mechanical properties to provide a display with a 2 mm pitch between the pixels and good conformability. At an operating supply voltage of 7 V, the average brightness of the display exceeds 170 cd/m2

Flexible large-area ultrasound arrays for medical applications made using embossed polymer structures

With the huge progress in micro-electronics and artificial intelligence, the ultrasound probe has become the bottleneck in further adoption of ultrasound beyond the clinical setting (e.g. home and monitoring applications). Today, ultrasound transducers have a small aperture, are bulky, contain lead and are expensive to fabricate. Furthermore, they are rigid, which limits their integration into flexible skin patches. New ways to fabricate flexible ultrasound patches have therefore attracted much attention recently. First prototypes typically use the same lead-containing piezo-electric materials, and are made using micro-assembly of rigid active components on plastic or rubber-like substrates. We present an ultrasound transducer-on-foil technology based on thermal embossing of a piezoelectric polymer. High-quality two-dimensional ultrasound images of a tissue mimicking phantom are obtained. Mechanical flexibility and effective area scalability of the transducer are demonstrated by functional integration into an endoscope probe with a small radius of 3 mm and a large area (91.2×14 mm2) non-invasive blood pressure sensor.</p

레이저 직접묘화법으로 프로그래밍 가능한 a-InGaZnO 게이트 어레이

게이트 어레이는 서로 연결되어 있지 않은 형태로 사전 제작된 트랜지스터 또는 논리 게이트 배열 위에 단 하나의 금속 층을 설계 및 추가함으로서 사용자가 원하는 회로를 제작할 수 있는 반 주문 제작 방식이다. 완전 주문 방식에 비해 개발 비용이 적고 prototype turnaround 기간이 짧다는 장점 덕분에 유연 인쇄 전자 분야에서 연구되고 있다. 지금까지 대부분의 연구는 유기 트랜지스터 기반 소자 배열을 제작한 다음, 몇몇 소자를 잉크젯 인쇄된 금속 배선으로 연결하여 다양한 유연 전자 회로를 제작할 수 있다는 것을 보여주었다. 허나, 아직까지 유기 박막 트랜지스터보다 전기적 성능과 균일도가 뛰어나다고 알려져 있는 a-InGaZnO 박막 트랜지스터를 사용하여 게이트 어레이를 구현한 사례는 없다. 이번 연구에서는 a-InGaZnO 박막 트랜지스터를 사용하여 게이트 어레이를 설계 및 제작하고 그 위에 단위 소자를 연결하는 배선을 레이저 직접묘화법으로 인쇄하여 디지털 회로를 구현함으로써 게이트 어레이의 프로그래밍 가능성을 보여준다. 게이트 어레이 설계에는 a-InGaZnO 박막 트랜지스터로 회로를 제작할 때 높은 노이즈 마진을 갖게 해준다고 알려져 있는 pseudo-CMOS 구조가 사용되었다. 더 나아가, 논리 회로의 면적을 줄이는 방법으로 하나의 dual-gate 트랜지스터 소자를 두 개의 병렬 연결된 트랜지스터로 사용하여 새로운 구조의 pseudo-CMOS NOR gate를 제안하고 그 NOR gate를 기본 소자로 하여 게이트 어레이를 제작하였다. 최종적으로, 레이저 직접묘화법으로 인쇄된 90 m 폭의 배선으로 8개의 NOR gate 를 연결하여 negative-edge-triggered D flip-flop 을 제작하고 3 V 의 공급 전압과 200 Hz 의 input 신호가 들어왔을 때, 1 ms 미만의 delay time을 보이며 성공적으로 동작하는 것을 확인하였다. 우리는 이번 연구를 통해 프로그래밍 가능한 게이트 어레이의 단위소자로써 a-IGZO 트랜지스터의 활용 가능성을 보여주었고 제안된 유연 전자 회로 제작 방식이 사물 인터넷이나 부착형 전자기기에 필수적인 디지털 회로의 설계 및 제작에 새로운 길을 열 것이라 기대한다.2

Active-matrix IGZO array with printed thermistor for large-area thermal imaging

Thermal imagers conventionally consist of a suspended sensing element on support structure with patterned thermal detection layer to get good thermal isolation between sensor elements[1]. Large area and wearable thermal imaging applications require cost effective fabrication, robustness and a flexible form factor. We present a 16×16 active-matrix IGZO array integrated with a screen printed thermistor on a thin and flexible substrate. Screen printing of the thermistor together with a flat-panel compatible backplane technology provides a cost effective and scalable route to large area thermal imaging. Unlike conventional focal plane arrays and microbolometers, in this work no suspended structures are used. Thus, the challenge is to get sufficient thermal separation between the imager elements, in particular when the thermistor is a single, non-structured layer extending across the entire backplane. The thermal response is determined by the thermal detection layer and the substrate, limiting the thermal response time τ = C/G, with C the thermal capacitance and G the thermal conductance. We show that by integration on thin polyimide film the thermal time constant improves by a factor of 30 compared to the same thermistor array on glass. In addition, we show that the thermal response can be further improved by reducing the thickness of (mainly) the printed thermistor layer. A stretchable form factor can be achieved through the formation of thermistor islands, connected by meander-shaped interconnects, enabling large area thermal imaging on conformal surfaces down to millimeter spatial resolution

Programmable a-InGaZnO Gate Array with Laser-Induced Forward Transfer

1