Some BSIM4 paprameters ?

Below is the MicroWind parameters for BSIM4 for 0.18 foundry. I know some of these like toxe= oxide thickness but the bold one I don't know. Can anybody help me


*
*BSIM4 parameters
*Nmos
*
*Low leakage
NMOS
b4vtho = 0.55
b4k1 = 0.17
b4k2 = 0.1
b4xj = 1.7e-7
b4nfact = 1.69b4toxe = 4e-9
b4ndep = 1.8e-17
b4d0vt = 2.3
b4d1vt = 0.54
b4vfb = -0.9
b4u0 = 0.038
b4ua = 2.8e-15
b4uc = -0.047e-15
b4vsat = 80e3
b4pscbe1 = 320e6
b4ute = -1.8
b4kt1 = -0.06
b4lint = -0.01e-6
b4wint = 0.02e-6
b4xj = 1.5e-7
b4ndep = 1.7e17
b4pclm = 0.29
*
*Pmos BSIM4
*
PMOS
b4vtho = 0.5
b4k1 = 0.29
b4k2 = 0.1
b4xj = 1.7e-7
b4nfact = 2.0
b4toxe = 4e-9
b4ndep = 1.8e17
b4d0vt = 2.3
b4d1vt = 0.54
b4vfb = 0.9
b4nfact = 2.2
b4u0 = 0.01
b4ua = 1e-15
b4uc = -0.047e-15
b4vsat = 60e3
b4pscbe1 = 320e6
b4ute = -1.8
b4kt1 = -0.06
b4lint = -0.04e-6
b4wint = 0.02e-6
b4xj = 1.5e-7
b4ndep = 1.7e17
b4pclm = 0.3
*
*MicroWind simulation parameters
*
deltaT = 0.5e-12 (minimum simulation*interval dT)
vdd =2.0
temperature = 27
rise time = 0.05
*
*End CMOS 0.18 µm
*
*

Not all, only the bold one

check out the bsim4 manual in the bsim4 berkeley page.