High-efficiency micro-energy generation based on free-carrier-modulated ZnO:N piezoelectric thin films

Lee, Eun‐Ju; Park, Jaedon; Yim, Munhyuk; Jeong, Sangbeom; Yoon, Giwan

doi:10.1063/1.4880935

Cited by 30 publications

(25 citation statements)

References 28 publications

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“…Therefore, the built-in electric field near the junction boundary effectively depletes excess electrons in the ZnO layer, which in turn reduces the screening effects for the generated piezopotential, leading to an enhanced piezoelectric output voltage and current. Secondly, the reliable Schottky barrier is another key factor greatly affecting the device output characteristics due to the leakage current through the interface [16,35]. In our work, the energy harvesting device uses a semiconductor p-n junction, rather than a metal-semiconductor Schottky barrier [36].…”

Section: Resultsmentioning

confidence: 99%

Piezoelectric performance enhancement of ZnO flexible nanogenerator by a NiO–ZnO p–n junction formation

et al. 2015

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Section: Resultsmentioning

confidence: 99%

Piezoelectric performance enhancement of ZnO flexible nanogenerator by a NiO–ZnO p–n junction formation

et al. 2015

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“…Figure 7 shows a cross-sectional view of the SiO 2 layer sandwiched between the top and bottom ZnO layers. The inset in the figure shows a high-resolution transmission electron microscopy (HRTEM) image and selected area electron diffraction (SAED) pattern of the ZnO film, indicating that the ZnO film has a crystalline form [15]. The distance between the (0002) planes was found to be 0.26 nm.…”

Section: Resultsmentioning

confidence: 99%

“…Their fabrication seems to be cost-effective because all that is required to fabricate these micro-energy generators is simply the stacking of thin film layers. Similarly, high-efficiency piezoelectric ZnO-based nanogenerators have also been developed for energy harvesting applications by forming ZnO/AlN-stacked layers [14] and adopting free-carrier-modulated ZnO:N piezoelectric thin films [15]. Moreover, there have been attempts to improve the piezoelectric materials or the device performance by adopting new electrodes or forming a p-n junction to block the screening effect based on energy band considerations [15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

“…This reduces the net potential across the ZnO film, thus degrading device performance. Therefore, to maximize the device output performance, it is essential to suppress the screening effect more effectively by controlling the ZnO free carrier density [15]. Some research teams have used insulators or other semiconductor materials to form a good potential barrier to increase output voltages [19].…”

Section: Introductionmentioning

confidence: 99%

“…Similarly, high-efficiency piezoelectric ZnO-based nanogenerators have also been developed for energy harvesting applications by forming ZnO/AlN-stacked layers [14] and adopting free-carrier-modulated ZnO:N piezoelectric thin films [15]. Moreover, there have been attempts to improve the piezoelectric materials or the device performance by adopting new electrodes or forming a p-n junction to block the screening effect based on energy band considerations [15][16][17][18]. The screening effect means that the piezoelectric potential (piezopotential) induced through the piezoelectric ZnO film is canceled by free electrons that exist inherently in a semiconductive ZnO material or electrode.…”

Section: Introductionmentioning

confidence: 99%

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Formation and Characterization of Various ZnO/SiO2-Stacked Layers for Flexible Micro-Energy Harvesting Devices

2018

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Abstract:In this paper, we present a study of various ZnO/SiO 2 -stacked thin film structures for flexible micro-energy harvesting devices. Two groups of micro-energy harvesting devices, SiO 2 /ZnO/SiO 2 micro-energy generators (SZS-MGs) and ZnO/SiO 2 /ZnO micro-energy generators (ZSZ-MGs), were fabricated by stacking both SiO 2 and ZnO thin films, and the resulting devices were characterized. With a particular interest in the fabrication of flexible devices, all the ZnO and SiO 2 thin films were deposited on indium tin oxide (ITO)-coated polyethylene naphthalate (PEN) substrates using a radio frequency (RF) magnetron sputtering technique. The effects of the thickness and/or position of the SiO 2 films on the device performance were investigated by observing the variations of output voltage in comparison with that of a control sample. As a result, compared to the ZnO single-layer device, all the ZSZ-MGs showed much better output voltages, while all the SZS-MG showed only slightly better output voltages. Among the ZSZ-MGs, the highest output voltages were obtained from the ZSZ-MGs where the SiO 2 thin films were deposited using a deposition power of 150 W. Overall, the device performance seems to depend significantly on the position as well as the thickness of the SiO 2 thin films in the ZnO/SiO 2 -stacked multilayer structures, in addition to the processing conditions.

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Wearable and Ultrasensitive Strain Sensor Based on High‐Quality GaN pn Junction Microwire Arrays

Cheng

Han

Cao

et al. 2020

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With the rapid growth in wearable electronics sensing devices, flexible sensing devices that monitor the human body have shown great promise in personalized healthcare. In the study, high-quality GaN pn junction microwire arrays with different aspect ratios and large-area uniformity are fabricated through an easy, repeatable fabrication process. The piezoelectric coefficient (d 33 ) of GaN pn junction microwire arrays increases from 7.23 to 14.46 pm V −1 with the increasing of the aspect ratio, which is several times higher than that of GaN bulk material. Furthermore, flexible ultrasensitive strain sensor based on GaN microwires with the highest d 33 is demonstrated to achieve the maximum open circuit voltage of 10.4 V, and presents excellent durability with stable output signals over 10 000 cycles with a response time of 50 ms. As a flexible and wearable sensor attached to the human skin, the GaN microwire pn junction arrays with such a high degree of uniformity can precisely monitor subtle human pulse and motions, which show great promise in future personalized healthcare.The piezoresistive strain sensors are unquestionably promising candidates for wearable and real-time human motiondetecting devices, [15,16] and they can be sensitive enough for even 10 nm vibration, [17] but the piezoelectric sensors are more prospective for self-powered devices owing to the piezoelectric effect of materials, defined as the occurrence of polarization when the material is subjected to external stress as a result of the separation of the positive and negative gravity centers of the molecules. Lead zirconate titanate (PZT) and polyvinylidene fluoride (PVDF) are the most commonly used piezoelectric mediums for piezoelectric sensors due to their high piezoelectric coefficients (d 33 ). [18][19][20][21] However, the toxic lead component in PZT and the high impedance of PVDF have limited their applications in wearable piezoelectric devices. [22,23] In this regard, semiconductor-based piezoelectric strain sensors represented by zinc oxide (ZnO) and GaN have been extensively studied as a result of their mechanical and chemical stability as well as environmental and biological compatibility. [24][25][26][27][28] In addition to the above advantages of the semiconductor, GaN exhibits merits of easy control of carrier concentration doping and higher stability compared to ZnO, while internal free carriers reduce the output of the device by screening the piezoelectric polarization, which is called free carriers screening. Suppressing the free carriers screening is undoubtedly an effective approach to improve the piezoelectric performance of the devices. [27,29,30] Another method is replacing the bulk or film materials with nanowires (NWs) considering the superior mechanical properties, large aspect ratio, and high energy conversion efficiency of NWs as compared to bulk materials. [31][32][33][34][35] For instance, Kacimi et al. fabricated a flexible strain sensor exhibiting 2 V peak outputs with vertically aligned ultra-long GaN wires, [36] ...

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High-efficiency micro-energy generation based on free-carrier-modulated ZnO:N piezoelectric thin films

Cited by 30 publications

References 28 publications

Piezoelectric performance enhancement of ZnO flexible nanogenerator by a NiO–ZnO p–n junction formation

Piezoelectric performance enhancement of ZnO flexible nanogenerator by a NiO–ZnO p–n junction formation

Formation and Characterization of Various ZnO/SiO2-Stacked Layers for Flexible Micro-Energy Harvesting Devices

Wearable and Ultrasensitive Strain Sensor Based on High‐Quality GaN pn Junction Microwire Arrays

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