• Proceedings of the Korean Vacuum Society Conference
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• 2008.02a
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• pp.279-279
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• 2008

• Proceedings of the Materials Research Society of Korea Conference
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• 2006.11a
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• pp.14.2-14.2
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• 2006

• Transactions on Electrical and Electronic Materials
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• v.9 no.1
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• pp.12-15
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• 2008

Hafnium oxynitride films have been deposited onto a silicon substrate by means of radio frequency (RF) reactive sputtering using a hafnium dioxide $(HfO_2)$ target with a variety of nitrogen! argon $(N_2/Ar)$ gas flow ratios. Auger electron spectroscopy (AES)results confirm that $N_2$ was successfully incorporated into the HfON films. An increase in the $N_2/Ar$ gas flow ratio resulted in metal oxynitride formation. The films prepared with a $N_2/Ar$ flow ratio of 20/20 sccm show (222), (530), and (611) directions of $HfO_2N_2$, and the (-111), (311) directions of $HfO_2$. From X-ray reflectometry measurements, it can be concluded that with $N_2$ incorporated into the HfON films, the film density increases. The density increases from 9.8 to $10.1g/cm^3$. XRR also reveals that the surface roughness is related to the $N_2/Ar$ flow ratio.

• Proceedings of the Korean Vacuum Society Conference
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• 2011.02a
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• pp.199-199
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• 2011

Recently, Thin film transistors (TFTs) with amorphous oxide semiconductors (AOSs) can offer an important aspect for next generation displays with high mobility. Several oxide semiconductor such as ZnO, $SnO_2$ and InGaZnO have been extensively researched. Especially, as a well-known binary metal oxide, tin oxide ($SnO_2$), usually acts as n-type semiconductor with a wide band gap of 3.6eV. Over the past several decades intensive research activities have been conducted on $SnO_2$ in the bulk, thin film and nanostructure forms due to its interesting electrical properties making it a promising material for applications in solar cells, flat panel displays, and light emitting devices. But, its application to the active channel of TFTs have been limited due to the difficulties in controlling the electron density and n-type of operation with depletion mode. In this study, we fabricated staggered bottom-gate structure $SnO_2$-TFTs and patterned channel layer used a shadow mask. Then we compare to the performance intrinsic $SnO_2$-TFTs and doping hafnium $SnO_2$-TFTs. As a result, we suggest that can be control the defect formation of $SnO_2$-TFTs by doping hafnium. The hafnium element into the $SnO_2$ thin-films maybe acts to control the carrier concentration by suppressing carrier generation via oxygen vacancy formation. Furthermore, it can be also control the mobility. And bias stability of $SnO_2$-TFTs is improvement using doping hafnium. Enhancement of device stability was attributed to the reduced defect in channel layer or interface. In order to verify this effect, we employed to measure activation energy that can be explained by the thermal activation process of the subthreshold drain current.

• Nuclear Engineering and Technology
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• v.25 no.1
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• pp.71-79
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• 1993

Positron annihilation characteristics and microhardness of 25% cold worked and isochronally annealed hafnium specimens were measured to study recovery and recrystallization stages of hafnium specimens. The annihilation lifetime of positrons in hafnium has been measured for the distinct cases of annihilation in the annealed lattice and annihilation after trapping at lattice defects generated by cold deformation at room temperature. The annihilation lifetime in the annealed lattice was 187 $\pm$3.7 psec, whereas it was 217 $\pm$ 4.2 psec for positrons trapped at deformation-induced defects (mostly dislocations). The changes in Doppler broadening and hardness showed similar trend in the recrystallization range, however, the measured value of Doppler broadening variation were quite sensitive to changes in the recovery region in which the variation in hardness value was completely insensitive. Recovery of cold worked hafnium initiated at about 623 K and recrystallization occurred at around 1023 K.

• Transactions on Electrical and Electronic Materials
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• v.17 no.6
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• pp.355-358
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• 2016

We present the alignment characteristics of LC (liquid crystal) molecules on solution-derived HLO (hafnium lanthanum oxide) films fabricated using IB (ion-beam) irradiation. We then demonstrated that LC molecules can be homogeneously and uniformly aligned on the HLO film irradiated at an IB incident energy of 1.2 keV. Physicochemical analysis methods such as atomic force microscopy and X-ray photoelectron spectroscopy were used to verify the LC alignment mechanism on the IB-irradiated HLO film. In addition, the electro-optical performance of a TN (twisted-nematic) cell fabricated using the IB-irradiated HLO film exhibited characteristics superior to those of the conventional TN cell fabricated using a rubbed polyimide layer.

• Proceedings of the International Microelectronics And Packaging Society Conference
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• 2002.05a
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• pp.198-202
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• 2002

$HfO_2$films were grown on Si substrate in the temperature range $250~550^{\circ}C$ using metal organic chemical vapor deposition (MOCVD) technique for a gate dielectric. Hafnium tart-butoxide and Oxygen gas were used as precursors and N2 was used as carrier gas. Impurity distribution and film structure(including interfacial layer) were studied at the deposition temperature range between 25$0^{\circ}C$ and $550^{\circ}C$. The growth rate and impurty distribution decreased with increasing temperature. The electrical properties of $HfO_2$were investigated with C-V, 1-V method and showed it has a good properties as a gate dielectric.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.9
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• pp.710-712
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• 2011

In this study, we fabricate resistive switching random access memory (ReRAM) devices constructed with a Al/$HfO_2$/ITO structure on glass substrates and investigate their memory characteristics. The hafnium oxide thin film used as a resistive switching layer is sputtered at room temperature in a sputtering system with a cooling unit. The Al/$HfO_2$/ITO device exhibits bipolar resistive switching characteristics, and the ratio of the high resistance (HRS) to low resistance states (LRS) is more than 60. In addition, the resistance ratio maintains even after $10^4$ seconds.

• Journal of the Korean Ceramic Society
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• v.52 no.6
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• pp.429-434
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• 2015

This study investigates the macroscopic wear behaviors of C/C and C/C-SiC composites coated with hafnium carbide (HfC). To improve the wear resistance of C/C composites, low-pressure chemical vapor deposition (LPCVD) was used to obtain HfC coating. The CVD coatings were deposited at various deposition temperatures of 1300, 1400, and $1500^{\circ}C$. The effect of the substrate material (the C/C substrate, the C/C-CVR substrate, or the C/C-SiC substrate deposited by LSI) was also studied to improve the wear resistance. The experiment used the ball-on-disk method, with a tungsten carbide (WC) ball utilized as an indenter to evaluate the wear behavior. The HfC coatings were found to effectively improve the wear resistance of C/C and C/C-SiC composites, compared with the case of a non-coated C/C composite. The former showed lower friction coefficients and almost no wear loss during the wear test because of the presence of hard coatings. The wear scar width was relatively narrower for the C/C and C/C-SiC composites with hafnium coatings. Wear behavior was found to critically depend on the deposition temperature and the material. Thus, the HfC-coated C/C-SiC composites fabricated at deposition temperatures of $1500^{\circ}C$ showed the best wear resistance, a lower friction coefficient, and almost no loss during the wear test.

• Proceedings of the Korean Vacuum Society Conference
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• 2010.08a
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• pp.110-110
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• 2010

현재 박막 트랜지스터는 비정질 실리콘 기반의 개발이 주를 이루고 있으며, 이 비정질 실리콘은 성막공정이 간단하고 대면적에 용이하지만 전기적인 특성이 우수하지 않기 때문에 디스플레이의 적용에 어려움을 겪고 있다. 이에 따라 poly-Si을 이용한 박막 트랜지스터의 연구가 진행되고 있는데, 이는 공정온도가 높고, 대면적에의 응용이 어렵다. 따라서 앞으로 저온 공정이 가능하며 대면적 응용이 용이한 박막 트랜지스터의 연구가 필수적이다. 한편 최근 박막 트랜지스터의 채널층으로 사용되는 물질에는 oxide 기반의 ZnO, SnO2, In2O3 등이 주로 사용되고 있고, 보다 적합한 채널층을 찾기 위한 연구가 많이 진행되어 왔다. 최근 Hosono 연구팀에서 IGZO를 채널층으로 사용하여 high mobility, 우수한 on/off ratio의 특성을 가진 소자 제작에 성공함으로써 이를 시작으로 IGZO의 연구 또한 세계적으로 활발한 연구가 이루어지고 있다. 특히, ZnO는 wide band gap (3.37eV)을 가지고 있어 적외선 및 가시광선의 투과율이 좋고, 전기 전도성과 플라즈마에 대한 내구성이 우수하며, 낮은 온도에서도 성막이 가능하다는 특징을 가지고 있다. 그러나 intrinsic ZnO 박막은 bias stress 같은 외부 환경이 변했을 경우 전기적인 성질의 변화를 가져올 뿐만 아니라 고온에서의 공정이 불안정하다는 요인을 가지고 있다. ZnO의 전기적인 특성을 개선하기 위해 본 연구에서는 hafnium을 doping한 ZnO을 channel layer로 소자를 제작하고 전기적 특성을 평가하였다. 이를 위해 DC magnetron sputtering을 이용하여 ZnO 기반의 박막 트랜지스터를 제작하였다. Staggered bottom gate 구조로 ITO 물질을 전극으로 사용하였으며, 제작된 소자는 semiconductor analyzer를 이용하여 출력특성과 전이 특성을 평가하였으며, ZnO channel layer 증착시 hafnium이 도핑 되는 양을 조절하여 소자를 제작한 후 intrinsic ZnO의 소자 특성과 비교 분석하였다. 그 결과 hafnium을 doping 시킨 소자의 field effect mobility가 $6.42cm^2/Vs$에서 $3.59cm^2/Vs$로 낮아졌지만, subthreshold swing 측면에서는 1.464V/decade에서 0.581V/decade로 intrinsic ZnO 보다 좋은 특성을 나타냄을 알 수 있었다. 그리고 intrinsic ZnO의 경우 외부환경에 대한 안정성 문제가 대두되고 있는데, hafnium을 도핑한 ZnO의 경우 temperature, bias temperature stability, 경시변화 등의 다양한 조건에서의 안정성이 확보된다면 intrinsic ZnO 박막트랜지스터의 문제점을 해결할 수 있는 물질로 될 것이라고 기대된다.