| Terahertz waves have many excellent characteristics and great application value.They have broad application potential in astronomical detection,atmospheric remote sensing,materials science,security applications,biomedicine,radar systems,and wireless communications.With the development of semiconductor technology and solid-state integrated circuits,more and more researchers have turned their attention to terahertz solid-state technology.The monolithic integration will be the main form of terahertz solid-state circuit development in the future.The planar Schottky barrier diode has the advantages of less device parasitic,high integration,good reliability,and room temperature operation,which make it widely used in terahertz monolithic integrated circuits.However,the increase in operating frequency and the shrinking of the physical size of device circuits have brought greater technical difficulties and challenges to terahertz monolithic integrated circuits.This dissertation divides the key issues affecting the performance of terahertz monolithic integrated circuits into the following four aspects.First,how to accurately model the Schottky barrier diode and measure the model parameters on-chip.Second,how to improve the operating frequency and power characteristics of the Schottky barrier diode,i.e.,reducing parasitic,improving efficiency,and increasing power capacity.Third,how to reduce the loss caused by the transmission structure at high frequencies and achieve low-loss planar transmission of terahertz waves.Fourth,how to improve the accuracy,bandwidth and efficiency of circuit design according to circuit requirements.Focusing on the above key issues,this dissertation will conduct systematic research on Schottky barrier diode-based terahertz monolithic integration technology,which includes Schottky diode design and implementation,Schottky diode parameter extraction and modeling,design of new Schottky diodes and terahertz transmission structures,terahertz monolithic integrated circuit process development,and terahertz monolithic integrated circuit design method.The main research contents include:(1)Research on the parameter extraction method of the diode on-chip measurement.The accuracy of the diode simulation model is a key factor affecting the design accuracy of terahertz monolithic integrated circuits.Aiming at this characteristic,the on-chip measurement method and de-embedding structure design of S-parameters of terahertz diodes are systematically studied.After a detailed analysis and summary of parasitic sources and effects in the measurement,a parameter extraction method named "Two-step Six-Structure Parameter Extraction Method(TSPEM)" was proposed.Combined with the S-parameter measured data,this method removes the parasitic introduced by the test pad through two de-embedding auxiliary structures,and then extracts the diode parameters,especially the diode junction capacitance Cj,through four parametric extraction auxiliary structures.The simulation model established by the parameters extracted in this method greatly removes the influence of peripheral parasitic,more accurately characterizes the intrinsic varactor characteristics of the diode,and then guides the simulation of terahertz monolithic integrated circuits.(2)Research on high-frequency diodes.A systematic study on how to reduce the intrinsic junction capacitance and how to reduce the parasitic coupling capacitance is carried out,and a T-junction substrate-free polymer film diodes is proposed.A T-junction can achieve an anode contact with a minimum diameter of 0.2 μm,corresponding to a minimum zero-bias junction capacitance of 0.15 f F.The substrate-less polymer film single mesa structure eliminates the diode substrate coupling and further reduces the coupling capacitance Cpp between the pads by removing the anode mesa and high aspect ratio metal fingers,and the corresponding coupling capacitance Cpp can reach a minimum of 0.13 f F.The T-junction substrate-less polymer film diode greatly reduces the highfrequency parasitic and junction capacitance of the device,which provides valuable technical support for the high-frequency circuit application of terahertz diodes.(3)Research on high-efficiency and high-power diodes.How to improve the frequency multiplication efficiency and maximum output power have always been an important research direction of terahertz frequency multiplication technology.By systematically studying the charge distribution inside the semiconductor,the inverted trapezoidal epitaxial cross-section Schottky diode and the interdigitated Schottky diode are proposed,realizing the high efficiency and high power output of the frequency multiplier,respectively.The inverted trapezoidal epitaxial cross-section Schottky diode eliminates the edge effect of the depletion layer,and the variable capacitance ratio of the junction capacitance is increased by about 15%;the conversion efficiency of the doubler based on this structure is also improved by about 15%.The interdigitated Schottky diode achieves four times the number of dies compared to the traditional structure by introducing auxiliary mesas on both sides under the same length.The frequency multiplier based on this structure can increase the maximum output power by more than300%.(4)Research on the transport structure of polymer films.Aiming at the problem that the transmission loss of the terahertz signal in the planar transmission structure becomes more and more obvious as the frequency increases,a polymer film transmission structure is proposed and realized.The low-k polymer film,which is passivated in the device process,is used as the circuit substrate,which completely removes the influence of the semiconductor substrate with a high dielectric constant.At the same time,the transmission structure of the polymer film is less likely to generate high-order modes,and a larger dynamic range of characteristic impedance of the transmission structure can be obtained.Compared with the Ga As substrate transmission structure,the proposed transmission loss can be reduced by about 50%,and the characteristic impedance variation range is increased by 50%-100%.(5)Research on terahertz circuit design method.Aiming at the advantage that devices in monolithic integrated circuits can be changed according to circuit requirements,a device-circuit integration design method(DCIDM)is proposed.This method introduces device structure design and intrinsic parameter design into the circuit design process,which can improve the design flexibility and optimization space,reduce the diode matching difficulty,and improve the circuit convergence,stability and versatility.At the same time,a harmonic impedance optimization method based on impedance function(FHIOM)is proposed to meet the impedance matching requirements of broadband frequency multipliers.This method can quickly obtain the optimal input and output embedded impedance of the frequency multiplier,and innovatively estimates the impedance of the matching structure through the formula,which strengthens the connection between the impedance optimization and the realization of the matching structure,and enables the matching structure to achieve a wider range of matching bandwidth.These two approaches lay the foundation for efficient broadband terahertz monolithic integrated circuit design.(6)Research on terahertz monolithic integration technology.Aiming at the tape-out realization of terahertz circuits,a set of diode and circuit structure design and processing platforms based on different material systems are established.Through the overall design process of device design and implementation,device parameter modelling,circuit design and implementation,and circuit performance is optimized to the greatest extent.Based on the process,terahertz monolithic integrated circuits such as a 0.1-110 GHz broadband mixing chip,a 0.75-1.1 THz monolithic integrated frequency mixing circuit,and a 280-295 GHz monolithic integrated frequency triple circuit are designed,which can provide a valuable experience for the future terahertz monolithic integrated circuits design and implementation. |
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