BaTi03 with and without Hf incorporation was studied as charge-trapping layer (CTL) for flash memory applications. Comparing with the device with BaTi03 CTL, the one with Hf-doped BaTi03 shows better performance in terms of higher program speed and better data retention due to suppressed leakage by Hf incorporated in BaTi03• Therefore, the Hf-doped BaTi03 is a promising candidate as CTL for flash memory application.published_or_final_versio

Huang, X

Lai, PT

X. D. Huang

P. T. Lai

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Improved performance of Hf-doped BaTiO&lt;inf&gt;3&lt;/inf&gt; as charge-traping layer for flash memory applications

BaTi03 with and without Hf incorporation was studied as charge-trapping layer (CTL) for flash memory applications. Comparing with the device with BaTi03 CTL, the one with Hf-doped BaTi03 shows better performance in terms of higher program speed and better data retention due to suppressed leakage by Hf incorporated in BaTi03• Therefore, the Hf-doped BaTi03 is a promising candidate as CTL for flash memory application.link_to_subscribed_fulltex

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Title Improved performance of Hf-doped BaTiO3 as charge-trapinglayer for flash memory applicationsAuthor(s) Huang, X; Lai, PTCitationThe 2013 IEEE International Conference of Electron Devices andSolid-State Circuits (EDSSC), Hong Kong, 3-5 June 2013. InConference Proceedings, 2013, p. 1-2Issued Date 2013URL http://hdl.handle.net/10722/191663Rights IEEE Conference on Electron Devices and Solid-State CircuitsProceedings. Copyright © IEEE.Improved Performance of Hf-Doped BaTi03 as Charge­Traping Layer for Flash Memory Applications x. D. Huang, P. T. Lai Department of Electrical and Electronic Engineering The University of Hong Kong Hong Kong, China laip@eee.hku.hk Abstract-BaTi03 with and without Hf incorporation was studied as charge-trapping layer (CTL) for flash memory applications. Comparing with the device with BaTi03 CTL, the one with Hf-doped BaTi03 shows better performance in terms of higher program speed and better data retention due to suppressed leakage by Hf incorporated in BaTi03• Therefore, the Hf-doped BaTi03 is a promising candidate as CTL for flash memory application. Keywords-flash memory;cllarge-trapping layer;Hf-doped BaTi03 I. INTRODUCTION High-k dielectrics have been widely proposed to take the place of Si3N4 as charge-trapping layer (CTL) in metal­oxide-nitride-oxide-silicon (MONOS)-type flash memories for down-scaling the dimensions as well as improving the performance of the devices [1]-[4]. Among various high-k dielectrics, BaTi03 is a promising candidate as CTL due to its high dielectric constant, which can enhance the electric field across the Si02 tunneling layer, thus improving program/erase (PIE) speeds at low operating voltage [2], [5]. Moreover, it has a large conduction-band offset with respect to the Si02 tunneling oxide, which is desirable for good retention because the tunneling probability of electrons from the CTL to the substrate decreases exponentially with the barrier height under retention mode [2], [5]. Also, it has been widely reported that the substitution of Ti4+ in BaTi03 with other iso:valent ions (e.g. Ht+, Zr4+) can reduce the dielectric loss and improve the properties of the film [6], [7]. However, there has been no study focusing on Hf-doped BaTi03 as CTL. Therefore, based on MONOS capacitors, this work aims to study the charge-trapping characteristics of Hf-doped BaTi03 by comparison with BaTi03. II. EXPERIMENTS MONOS capacitor with AIIAIz03/Hf-doped BaTi03/Si02/Si was fabricated on p-type silicon substrate. After the standard RCA (Radio Corporation of America) cleaning, 2-nm Si02 as tunneling layer (TL) was grown on the wafers by thermal dry oxidation. Then 10-nm Hf-doped BaTi03 was deposited on the Si02 by co-sputtering using BaTi03 target at a power of 30 Wand Hf target at a power of 30 W in a mixed Ar/02 ambient, and the corresponding MONOS capacitor was denoted as Hf-BTO. Then 15-nm AI203 as blocking layer (BL) was deposited by means of atomic layer deposition using trimethyl-aluminum 978-1-4673-2523-3/13/$31.00 ©20 13 IEEE (AI(CH3)3) and H20 as precursors at 300°C. Finally, AI was evaporated and patterned as gate electrodes by wet etching followed by forming-gas annealing at 300 °C for 20 min. For comparison, a control sample with AIIAI20iBaTiOiSi02/Si structure (denoted as BTO) was also fabricated by the same process. All electrical tests were performed under a light­tight and electrically-shielded condition. III. RESULTS AND DlSSCUSI0N Fig. 1 displays the I-MHz C-V hysteresis loops of the MONOS capacitors with and without Hf incorporation. Sweep starts from inversion region to accumulation region, and back to inversion region again. As the sweeping voltage increases from ±8 V to ±12 V, the memory window increases from 4.0 V/3.9 V to 8.0 V17.7 V for the BTO and Hf-BTO samples respectively. The Hf-BTO sample shows similar memory as the BTO one. Therefore, it is believed that Hf incorporated in BaTi03 has little influence on the trap density of the BaTi03 film. .. � 0.8 .� 0.6 Co .. <.> ." 0.4 .� § 0.2 � 0.0 Solid symbol: Hf.BT·OO�_iBl_it:!9BE� Open sym I: BTO -10 -5 0 5 10 Voltage (V) Fig. I I-MHz C-V hysteresis curves of the MONOS capacitors with and without Hf incorporation. Fig. 2(a) shows the program transient characteristics of the MONOS capacitors with and without Hf incorporation, where the Hf-BTO sample displays higher program speed than the BTO one under the same operating conditions. As the operating voltage Va increases from +8 V to + 12 V with a pulse width of 100 /!s, the VFBshift of the Hf-BTO sample increases from 3.0 V to 5.3 V; for comparison, the VFB shift of the BTO one increases from 2.2 V to 4.6 V. Considering the similar memory window (thus similar trap density) for the two samples from Fig. 1, the higher program speed for the Hf-BTO sample should be due to its higher charge­trapping efficiency. Since Hf has better stability than Ti, Hf incorporated in BaTi03 is helpful to suppress the oxide leakage, thus contributing to the higher charge-trapping efficiency [4]. This claim can be further confirmed by the I­V characteristics of the MONOS capacitors, where the Hf­BTO sample shows smaller leakage (2.1xlO-8 A/cm2 at Va = +3 V) than the BTO one (4.0x 10-8 A/cm2 at V G = +3 V). Fig. 2(b) shows the erase transient characteristics of the samples, where both samples are programmed at +12 V for 1 s before the erase test. It is observed that the Hf-BTO sample exhibits lower erase speed than the BTO one under the same operating conditions. This should be due to its suppressed leakage by Hf incorporation; therefore, electrons trapped in the CTL are more difficult to de-trap into the substrate [3]. This inference can be further confirmed by the data retention property shown in Fig. 3 later. 7r----------------------" Solid symbol: Hf-BTO --"",,10 Open symbol: B� _  �;::::"'"" 6 _-- ____ �D ___ D � 5 � -0--0-+12 V � �. -.--0-+8 V �4 � >� e_e_e--:7 3�-- ___ 0/ �_o-o 2 ������������_ 104 104 10" 10" 10' Time(s) (a) 4�----�����--------, {rogram at +12 V, 1s before erase � Solid symbol: Hf-BTO :> .5 _ ___. Open symbol: BTO =- �, ---�. � ----.. >··6 0 � -0--0--12 V 0___. 0 _______ -7 -� 10· 10' 10' lime(s) (b) 10' Fig. 2 (a) Program and (b) erase transient characteristics for the MONOS capacitors with and without Hf incorporation. The neutral VFB for the BTO and Hf-BTO samples are -1.5 V and -1.3 V respectively. Fig. 3 displays the retention characteristics of the MONOS capacitors with and without Hf incorporation under program state measured at 85°C. To exclude the influence of Coulomb-repulsion effect on data retention, both samples are operated to obtain the same initial VFB shift (�4.6 V) for fair comparison. The retained charge rate after 10 years is evaluated by extrapolation to be 32.2 % and 45.2 % for the BTO and Hf-BTO samples respectively. The smaller charge­loss rate of the Hf-BTO sample demonstrates its better data retention. As mentioned above, Due to better thermal stability of Hf than that of Ti, Hf incorporated in BaTi03 can suppress the leakage, which is believed to be responsible for its better data retention. 100 -Ll"", LI:::::::� _80  � ��� "' ... CI> , ' E' 60 .... ... '" .:= U -.- Hf-BTO -g40 c � 20 -o- BTO 10 years' , , , , Fig. 3 Data retention for the BTO and Hf-BTO samples measured at 85°C. Both samples are programmed to achieve the same initial VFB shift (- 4.6 V). IV. CONCLUSIONS In summary, based on MONOS capacitors, the charge­trapping characteristics of the BaTi03 films with and without Hf incorporation were investigated. Comparing with the device with BaTi03 CTL, the one with Hf-doped BaTi03 CTL displays higher program speed and better data retention. Therefore, the Hf-doped BaTi03 is a promising candidate as CTL for flash memory applications. REFERENCES [ I] S. H. Lin, A. Chin, F. S. Yeh, and S. P. McAlister, "Good 150°C retention and fast erase charge-crapping-engineered memory with scaled ShN4," in iEDM Tech. Dig., 2008, pp. 843-846. [2] X. D. Huang, P. T. Lai, L. Liu, and J. P. Xu, "Nitrided SrTi03 as charge-trapping layer for nonvolatile memory applications," Appl. Phys. Lett., vol. 98, pp. 242905-1-242905-3, Jun. 20 I I. [3] J. Y.Wu, Y. T. Chen, M. H. Lin, and T. B. Wu, "Ultrathin HfON trapping layer for charge-trapping memory made by atomic layer deposition," iEEE Electron Devices Lett., vol. 31, pp. 993-995, Sep. 2010. [4] X. D. Huang, P. T. Lai, and Johnny K. O. Sin, "Performance of nonvolatile memory by using band-engineered SrTiOiHfDN stack as charge-trapping layer," Microelectron. Reliab., vol. 52, pp. 2527-2531, Nov., 2012. [5] G. D. Wilk, R. M. wallace, and J. M.Anthony, "High-K gate dielectrics: Current status and materials properties considerations," J Appl. Phys., vol. 89, pp. 5243-5275, May 2001. [6] H. Y. Tian, Y. Wang, J. Miao, H. L. W. Chan, and C. L. Choy, "Preparation and characterization of hafuium doped barium titanate ceramics," J Alloys Compd., vol. 431, pp. 197-202, Jun. 2006. [7] W. S. Choi, B. S. Jang, D. G. Lim, J. Vi, and B. Hong, "Characterization of Ba(Zro2 Tio8)03 thin films deposited by RF-magnetron sputtering," J Cryst. Growth, vol. 237-239, pp. 438-442, Apr. 2002. 

Improved performance of Hf-doped BaTiO3 as charge-traping layer for flash memory applications

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Improved performance of Hf-doped BaTiO3 as charge-traping layer for flash memory applications

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