Bahman Kheradmand Boroujeni

A Compact a-IGZO TFT Model Based on MOSFET SPICE

This letter presents a compact model for flexible analog/RF circuits design with amorphous indium-gallium-zinc oxide thin-film transistors (TFTs). The model is based on the MOSFET LEVEL=3 SPICE model template, where parameters are fitted to measurements for both dc and ac characteristics. The proposed TFT compact model shows good scalability of the drain current for device channel lengths ranging from 50 to 3.6 μm. The compact model is validated by comparing measurements and simulations of various TFT amplifier circuits. These include a two-stage cascode amplifier showing 10 dB of voltage gain and 2.9 MHz of bandwidth.

{\rm Level}=3

This paper presents a cascode amplifier for bendable analog and radio-frequency electronic systems in a flexible amorphous indium gallium zinc oxide (a-IGZO) TFT technology, featuring a minimum gate length of 5 μm. The design is optimized for large bandwidth. The circuit design was carried out with a MOSFET LEVEL=3 SPICE model template. The required model parameters were extracted from both DC and AC measured characteristics. Measurements results show 10.5 dB of voltage gain and a 3 dB bandwidth of 2.62 MHz; the small-signal performance was closely predicted by simulations. The presented circuit provides the highest frequency of operation reported for a single-stage cascode amplifier in a-IGZO TFT technology to date.

Template for Analog/RF Circuit Designs

This paper presents an operational amplifier based on pseudo-CMOS blocks and integrated in a flexible a-IGZO TFT technology. The circuit consists of only nMOS transistors, and the pair of active loads is in a pseudo-CMOS configuration. These active loads allow various kinds of common mode feedback schemes or cross-coupled connection, typical for CMOS operational amplifiers. The proposed amplifier is fabricated on a flexible film, and characterized with 5 V supply voltage and an output load capacitance of 15 pF. The measured open-loop gain is 22.5 dB, which is the highest reported for operational amplifiers in metal-oxide TFT technology. The measured bandwidth and gain bandwidth products are 5.6 kHz, and 31 kHz, respectively with 160 μW power consumption, which is lowest among flexible operational amplifies.

A 2.62 MHz 762 µW cascode amplifier in flexible a-IGZO thin-film technology for textile and wearable-electronics applications

This paper presents an AM receiver implemented in a flexible a-IGZO TFT technology. The circuit consists of a four-stage cascode amplifier at the RF input, a detector based on a source follower, and a common source circuit for the baseband amplification. The measured conversion gain is very flat and exceeds 15 dB from 2 to 20 MHz carrier frequency range, which covers a relevant portion of the shortwave radio band. The 3 dB-bandwidth of the audio signal is 400 Hz to 10 kHz, which is comparable to the so-called voice band, and it is also suitable to low-rate data communication. In addition, an integrated demonstration of the AM receiver and textile antennas is carried out. The flexible a-IGZO receiver successfully detected the baseband signal through the textile antennas, demonstrating for the first time wireless transmission for this class of technologies.

22.5 dB open-loop gain, 31 kHz GBW pseudo-CMOS based operational amplifier with a-IGZO TFTs on a flexible film

To our knowledge, this paper presents the first high-gain amplifiers fabricated in flexible self-aligned amorphous indium gallium zinc oxide (a-IGZO) thin-film-transistor (TFT) technology. For the common source amplifier applying positive feedback a voltage gain of 17 dB, a bandwidth of 79 kHz and a DC power of only 0.76 mW were measured. For the cascode amplifier a voltage gain of 25 dB voltage gain, a bandwidth of 220 kHz and a DC power of 2.32 mW were measured. The simulations based on a RPI-aTFT model are compared with measurements. The chip areas are 8 and 10 mm2, respectively.

15 dB conversion gain, 20 MHz carrier frequency AM receiver in flexible a-IGZO TFT technology with textile antennas

We developed a fully flexible AM (amplitude modulation) radio receiver suitable for integration in an “audio bag”, by exploiting the heterogeneous integration of several fully flexible technologies. In this paper, we present a 2.9 mW 2-bit digitally-controlled tuner with a 576 kHz tuning range, a 3.5 mW 1 MHz AM detector and their integration in such a fully-flexible system. Their optimized power consumptions are essential because thin flexible batteries and organic solar cells serve as power supply. The circuits are fabricated in a low-temperature amorphous indium gallium zinc oxide (a-IGZO) technology. For the system integration textile techniques as well as flexible inkjet-printed packages and printed circuit boards (IPCBs) were used.

High gain amplifiers in flexible self-aligned a-IGZO thin-film-transistor technology

This paper provides an overview of the research activities within the frame of the European project FLEXIBILITY. The project aims at advancing the competitiveness of Europe in the area of multifunctional, ultra-lightweight, ultra-thin, bendable organic and large area electronics (OLAE). An overview of the technologies available to the consortium is provided, together with details of the performance achieved by the first prototypes. Particular focus is given to the circuit design in technologies compatible with the flexible components and systems. Using a 50 MHz IGZO TFT technology, several circuits have been demonstrated, including a 20 MHz AM demodulator.

3.5mW 1MHz AM detector and digitally-controlled tuner in a-IGZO TFT for wireless communications in a fully integrated flexible system for audio bag

This paper presents a compact transistor model for circuit design in a flexible amorphous indium gallium zinc oxide (a-IGZO) thin-film transistor (TFT) technology. The presented model is technology specific and builds upon the Verilog-A Rensselaer Polytechnic Institute amorphous silicon TFT (RPI-aTFT) model. On the basis of extensive device characterization, we introduce appropriate new equations and parameters that enable an accurate and efficient behavioral representation of a-IGZO TFTs. In this work, we address the modelling of short channel effects, the scalability for channel lengths from 5 µm to 50 µm, as well as the presence of process variation. Using this model, a Cherry-Hooper amplifier is designed, analyzed, implemented in a flexible a-IGZO TFT technology, and characterized. Finally, to validate the presented transistor model, we compare circuit simulations and measurements of the Cherry-Hooper amplifier circuit. The amplifier provides a voltage gain of 9.5 dB and has a GBW of 7.2 MHz from a supply voltage of 6 V. The simulation using our new compact transistor model resembles the measured characteristics very well. It predicts a voltage gain of 10.4 dB and a GBW of 7.0 MHz.

Overview of the EC project FLEXIBILITY: Organic and thin-film ICs up to radio frequencies for multifunctional flexible systems

This paper presents an AM detector circuit in a bendable a-IGZO TFT technology. The circuit is based on a common-source stage loaded with a single-ended active inductor, which uses only one active transistor. This active inductor is the key element for the achieved circuit performance. The detector circuit consumes only 0.39 mW, which is almost a tenfold improvement over previous works in the same technology and crucial for mobile and wearable applications. At the same time it has the smallest chip area. The detector provides a conversion gain of 20.3 dB and an RF −3dB-bandwidth of around 7.5 MHz. At fc=13.56 MHz it has 11.6 dB gain, which also allows its use in this unlicensed ISM radio band for RFID and smart label applications.

A transistor model for a-IGZO TFT circuit design built upon the RPI-aTFT model

In this paper the recent progress of active high frequency electronics on plastic is discussed. This technology is mechanically flexible, bendable, stretchable and does not need any rigid chips. Indium Gallium Zinc Oxide (IGZO) technology is applied. At 2 V supply and gate length of 0.5 μm, the thin-film transistors (TFTs) yield a measured transit frequency of 138 MHz. Our scalable TFT compact simulation model shows good agreement with measurements. To achieve a sufficiently high yield, TFTs with gate lengths of around 5 μm are used for the circuit design. A Cherry Hopper amplifier with 3.5 MHz bandwidth, 10 dB gain and 5 mW dc power is presented. The fully integrated receiver covering a plastic foil area of 3 × 9 mm2 includes a four stage cascode amplifier, an amplitude detector, a baseband amplifier and a filter. At a dc current of 7.2 mA and a supply of 5 V, a bandwidth of 2 - 20 MHz and a gain beyond 15 dB were measured. Finally, an outlook regarding future advancements of high frequency electronics on plastic is given.