The width of depletion region in a varactor diode can be modulated by varying a reverse bias voltage. Thus, the preferred characteristics of depletion capacitance can obtained by the change in the width of depletion region so that it can select only the desirable frequencies. In this paper, the TV Tuner Varactor diode fabricated by hyper-abrupt profile control technique is presented. This diode can be operated within 3.3 V of driving voltage with capability of UHF band tuning.
To form the hyper-abrupt profile, firstly, p+ high concentration shallow junction with 0.2 ㎛ of junction depth and 1E+20 ions/㎝-3 of surface concentration was formed using BF2 implantation source. Simulation results optimized important factors such as epitaxial thickness and dose quality, diffusion time of n+ layer. To form steep hyper-abrupt profile, Formed n+ profile implanted the PH3 source at Si(100) n-type epitaxial layer that has resistivity of 1.4 Ωcm and thickness of 2.4 ㎛ using p+ high concentration Shallow junction. Aluminum containing to 1 % of Si was used as a electrode metal. Area of electrode was 30,200 ㎛2.. The C-V and Q-V electric characteristics were investigated by using impedance Analyzer (HP4291B). By controling of concentration profile by n+ dosage at p+ high concentration shallow junction, the device with maximum LF at ?1.5 V and 21.5 ∼ 3.47 pF at 0.3 ∼ 3.3 V was fabricated. We got the appropriate device in driving voltage 3.3 V having hyper abrupt junction that profile order (m factor) is about ?3/2. The deviation of capacitance by hyper abrupt junction with C0.3 V of initial capacitance is due to the deviation of thermal process y ion implantation and diffusion. The deviation of initial capacitance at 0.3 V can be reduced by control of thermal process tolerance using RTP on wafer. The deviation of capacitance at 3.3 V can be reduced by a process having minimized deviation of wafer thickness. The process make a uniform wafer thickness using etching oxide after growing up oxide on the silicon.
The result of C-V characteristics that obtained when sweeping 30 V and 3.3 V varactor diode device with reverse bias voltage (0 V ∼ 30 V), In the case of varactor diode which is driven at 30 V device, it obtained 15.3 pF capacitance at 2V and 2.29 pF capacitance at 25 V. On the other hand, in the case of varactor diode which is driven at 3.3 V, it obtained 21.5 pF capacitance at 0.3 V and 3.47 pF capacitance at 3.3 V. quality factor on the reverse bias voltage of varactor diode operating on 30 V grade and 3.3 V, the varactor diode driving on 30 V grade is the value of 29, 381 in operating voltage 2 V, 25 V. respectively that is viewed the similar level in comparison with the varactor diode driving on 3.3 V grade which is the value of 20, 313 in operating voltage 0.3 V, 3.3 V respectively. We had verified main characteristics and tested reliability with leakage current by reversed bias.