Inverted process for graphene integrated circuits fabrication

Benefit from exceptional electrical transport properties, graphene receives worldwide attentions, especially in the domain of high frequency electronics. Due to absence of effective bandgap causing off-state the device, graphene material is extraordinarily suitable for analog circuits rather than digital applications. With this unique ambipolar behavior, graphene can be exploited and utilized to achieve high performance for frequency multipliers. Here, dual-gated graphene field-effect transistors have been firstly used to achieve frequency quadrupling. Two Dirac points in the transfer curves of the designed GFETs can be observed by tuning top-gate voltages, which is essential to generate the fourth harmonic. By applying 200 kHz sinusoid input, arround 50% of the output signal radio frequency power is concentrated at the desired frequency of 800 kHz. Additionally, in suitable operation areas, our devices can work as high performance frequency doublers and frequency triplers. Considered both simple device structure and potential superhigh carrier mobility of graphene material, graphene-based frequency quadruplers may have lots of superiorities in regards to ultrahigh frequency electronic applications in near future. Moreover, versatility of carbon material system is far-reaching for realization of complementary metal-oxide-semiconductor compatible electrically active devices.

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confidence: 99%

A graphene based frequency quadrupler

Cheng

Huang

Mao

et al. 2017

“…However, even though the cutoff frequency ( f T ) of graphene field-effect transistors (GFETs) exceed Si transistors 3 4 , the maximum oscillation frequency ( f max ), as the most relevant metric to circuit performance, seriously lags behind. Promising circuit applications are limited in passive circuits 5 6 7 8 9 . Typical f max values are one order of magnitude lower than f T 3 10 11 12 13 .…”

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confidence: 99%

“…In this work, the modern CMOS back-end-of-line (BEOL) technology has been employed to fabricate deep-submicron GFETs. GFETs with gate lengths ranging from 100 nm to 400 nm have been fabricated on 200 mm wafers by recently reported passive-first-active-last inverted process 8 9 20 . In particular, buried gates with depth-to-width ratio up to six folds were achieved for the purpose of lowering the gate resistance.…”

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confidence: 99%

Deep-submicron Graphene Field-Effect Transistors with State-of-Art fmax

Lyu

Liu

et al. 2016

Self Cite

In order to conquer the short-channel effects that limit conventional ultra-scale semiconductor devices, two-dimensional materials, as an option of ultimate thin channels, receive wide attention. Graphene, in particular, bears great expectations because of its supreme carrier mobility and saturation velocity. However, its main disadvantage, the lack of bandgap, has not been satisfactorily solved. As a result, maximum oscillation frequency (fmax) which indicates transistors’ power amplification ability has been disappointing. Here, we present submicron field-effect transistors with specially designed low-resistance gate and excellent source/drain contact, and therefore significantly improved fmax. The fabrication was assisted by the advanced 8-inch CMOS back-end-of-line technology. A 200-nm-gate-length GFET achieves fT/fmax = 35.4/50 GHz. All GFET samples with gate lengths ranging from 200 nm to 400 nm possess fmax 31–41% higher than fT, closely resembling Si n-channel MOSFETs at comparable technology nodes. These results re-strengthen the promise of graphene field-effect transistors in next generation semiconductor electronics.

“…Poineering works on graphene circuits have led to the demonstration of frequency doublers 10 11 12 , ambipolor mixers 13 and modulators 14 15 , in which graphene’s unique property of electron and hole symmetry is utilized. By superimposing an sinusoidal signal on the minimum conductance point (Dirac point), the electron or the hole branches, the frequency and phase of the output signal could be modulated.…”

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confidence: 99%

“…On the other hand, graphene’s IC process has witnessed substantial improvements 12 19 22 . Both Han et al and the authors’ group have proposed the multi-layer-routing inverted process for graphene integration, which serves as the foundation for future novel graphene circuit architectures 12 19 22 . The inverted process utilizes CMOS BEOL processes to fabricate circuit and device structures, followed by CVD graphene transfer at the back end of the flow.…”

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confidence: 99%

Graphene Distributed Amplifiers: Generating Desirable Gain for Graphene Field-Effect Transistors

Lyu

Huang

et al. 2015

Self Cite

Ever since its discovery, graphene bears great expectations in high frequency electronics due to its irreplaceably high carrier mobility. However, it has long been blamed for the weakness in generating gains, which seriously limits its pace of development. Distributed amplification, on the other hand, has successfully been used in conventional semiconductors to increase the amplifiers’ gain-bandwidth product. In this paper, distributed amplification is first applied to graphene. Transmission lines phase-synchronize paralleled graphene field-effect transistors (GFETs), combining the gain of each stage in an additive manner. Simulations were based on fabricated GFETs whose fT ranged from 8.5 GHz to 10.5 GHz and fmax from 12 GHz to 14 GHz. A simulated four-stage graphene distributed amplifier achieved up to 4 dB gain and 3.5 GHz bandwidth, which could be realized with future IC processes. A PCB level graphene distributed amplifier was fabricated as a proof of circuit concept.